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Institutional Archive of the Naval Postgraduate School
Calhoun: The NPS Institutional Archive
DSpace Repository
Theses and Dissertations l. Thesis and Dissertation Collection, all items
1991-06
The Coast Guard's VHF-FM National Distress
System: analysis for recapitalization.
Glidden, William C.
Monterey, California. Naval Postgraduate School
http://hdl.handle.net/10945/28032
Downloaded from NPS Archive: Calhoun
Calhoun is the Naval Postgraduate School's public access digital repository for
| A8 D U DLEY research materials and institutional publications created by the NPS community.
dil Calhoun is named for Professor of Mathematics Guy K. Calhoun, NPS's first
w KNOX appointed — and published — scholarly author.
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NAVAL POSTGRADUATE SCHOOL
Monterey, California
THESIS
THE COAST GUARD'S
VHF-FM NATIONAL DISTRESS SYSTEM:
ANALYSIS FOR RECAPITALIZATION
rx дәг
by
William C. Glidden
June 1991
Advisor: Dan C. Boger
Approved for public release; distribution is unlimited.
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és7acSi
UNCLASSIFIED
SECURITY CLASSIFICATION OF THIS PAGE
Form Approved
REPORT DOCUMENTATION PAGE
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Approved for public release;
distribution is unlimited
2b. DECLASSIFICATION / DOWNGRADING SCHEDULE
4 PERFORMING ORGANIZATION REPORT NUMBER(S) 5 MONITORING ORGANIZATION REPORT NUMBER(S)
6a NAME OF PERFORMING ORGANIZATION 6b OFFICE SYMBOL
(if applicable)
AS
7a NAME OF MONITORING ORGANIZATION
Naval Postgraduate Schoo
6c. ADDRESS (City, State, and ZIP Code)
Naval Postgraduate School
7b ADDRESS (City, State, and ZIP Code)
Monterey, CA 93943-5000 Monterey, CA 93943-5000
8b OFFICE SYMBOL 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER
(If applicable)
8a. NAME OF FUNDING / SPONSORING
ORGANIZATION
10 SOURCE OF FUNDING NUMBERS
PROGRAM PROJECT TASK WORK UNIT
ELEMENT NO NO NO ACCESSION NO
8c. ADDRESS (City, State, and ZIP Code)
11 TITLE (Include Security Classification)
THE COAST GUARD'S VHF-FM NATIONAL DISTRESS
SYSTEM: ANALYSIS FOR RECAPITALIZATION
12. PERSONAL AUTHOR(S)
GLLDDEN . William C.
13a TYPE OF REPORT 13b TIME COVERED 14 DATE OF REPORT (Year, Month, Day)
Master's Thesi: ROM O 1991 June 180
li ". CUN The vievs expressed dn this thesis are those of the
puhon and do not reflect the official policy or position of the Depart-
ment of Defense or the US Government.
18 SUBJECT TERMS (Continue on reverse ıf necessary and identify by block number)
VHF-FM; National Distress System (NDS); Digital
HB ] 60 00 /)Selective Calling (DSC), high-sites; pocket
radio netvorks
19 ABSTRACT (Continue on reverse if necessary and identify by block number)Twenty years ago the U.S. Coast Guard
established the National Distress System (NDS) of VHF-FM remote-controlled transceivers
to provide nationwide maritime distress coverage and Coast Guard C communications. The
NDS was designed to provide radio coverage along the coasts, the inland waterways, and
the Great Lakes. The current NDS equipment is reaching the end of its useful life and
the new requirements placed upon the system havg mandated its replacement.
In this thesis the author first details the C structure of the Coast Guard and identi-
fies it major missions, and then relates history of the NDS. An examination of the NDS'
current Configuration is performed, the requirements are identified, and applicable
technology is explored.
The author concludes that present technology and commercially available equipment is
available to solve the present and anticipated requirements placed upon the NDS. The
[author provides a model of the proposed system and presents an implementation schedule
[for replacement of the NDS.
20 DISTRIBUTION / AVAILABILITY OF ABSTRACT 21 ABSTRACT SECURITY CLASSIFICATION
[ XuNcLassiriED/UNLIMITED | D] SAME AS RPT O OTIC USERS NCLA D
22a NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) | 22c OFFICE SYMBOL
BOGER, Dan C. 408-646-260 AS/Bo
DD Form 1473, JUN 86 Previous editions are obsolete SECURITY CLASSIFICATION OF THIS PAGE
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1
Approved for public release; distribution is unlimited.
The Coast Guard's
VHF-FM National Distress System:
Analysis for Recapitalization
by
William C. Slidden
Lieutenant, United States Coast Guard
B.A., The College of Wooster, 1974
M.Ed., Bowling Green State University, 1977
Submitted in partial fulfillment
of the requirements for the degree of
MASTER OF SCIENCE IN TELECOMMUNICATIONS SYSTEMS MANAGEMENT
from the
NAVAL POSTGRADUATE SCHOOL
June 1991
D. R. Whipple, airman,
Department of Adminis tive Sciences
ii
ABSTRACT
Twenty years ago the U. S. Coast Guard established the National Distress System
(NDS) of VHF-FM remote-controlled transceivers to provide nationwide maritime
distress coverage and Coast Guard C? communications. The NDS was designed to pro-
vide radio coverage along the coasts, the inland waterways, and the Great Lakes. The
current NDS equipment is reaching the end of its useful life and the new requirements
placed upon the system have mandated its replacement.
In this thesis the author first details the C? structure of the Coast Guard and identi-
fies its major missions, and then relates history of the NDS. An examination of the NDS'
current configuration is performed, the requirements are identified, and applicable
technology is explored.
The author concludes that present technology and commercially available equipment
is available to solve the present and anticipated requirements placed upon the NDS. The
author provides a model of the proposed system and presents an implementation schedule
for replacement of the NDS.
iil
I.
II.
INTRODUCTION ae AS
A. BACKOROUND ........
B. RESEARCH OBJECTIVE ..
C. RESEARCH APPROACH ..
D.
E. THESIS OUTLINE aza
TABLE OF CONTENTS
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IMPORTANCE TO THE COAST GUARD T. a ae
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1. Chapter II: Present Coast Guard C? Structure and Missions .....
2. Chapter III: National VHF-FM Distress System Background ....
3. Chapter IV: Established and Potential NDS Operational
Requirements ........
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4. Chapter V: Evaluation of Selected Technology ..............
5. Chapter VI: Summary and Recommendations ...............
PRESENT COAST GUARD C? STRUCTURE AND MISSIONS .........
A.
B.
COAST GUARD C” STRUCTURE.........................
1. Coast Guard Command and Control Structure ...............
2. Coast Guard Communications Structure ...................
COAST GUARD MISSIONS
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C. COAST GUARD PROGRAM MANAGER MISSION SUPPORT ...
NATIONAL VHF-FM DISTRESS SYSTEM BACKGROUND .........
An HISTORI OR THE NDS a y z ə o 0 a
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4. Public CommunicationS ............................. 31
CURRENT NDS CONFIGURATION ...................... 32
1. Architecture... . ... i i pp mp ии 32
2. Hardware .........6...0.0.0006 VU. ии 34
a. Transceivers ... n pp p P 7: 34
b. Remote Control Units әәә. әрли A 34
c. ."Antennas ... 55.5 eee DE 35
d. “Control and Communications Circuits ............... 35
3. Transceiver and Remote Control Locations................ 36
a. Equipment Locations AN 36
b. Geographical Coverage ə . 36
4. System Integration... EE EE —— 37
a. Connectivity Within the NDS Network .............. 37
b. Connectivity With Other Networks ................. 37
5. Non-Standard/Special NDS Installations ................. 38
a. Secure Communications” 577 38
b. Data Channel Usage ә 1T 38
c.. VHF-FM Direction Finding Installations ............. 39
LOCAL USE VHF-EM SYSTEMS E 39
1. Shore. Unit Fgupmen ENEE 39
2. Shore Unit VHF-FM RDF Capabilities .................. 40
a. Individual RDF sites Sme EE 40
vi
b. RON ei кардинал 40)
IV. ESTABLISHED AND POTENTIAL NDS OPERATIONAL
SUIS e eh ии батана 42
A. INTERNAL COAST GUARD NDS-RELATED REQUIREMENTS . 42
İSE lisied Feduismisnis «we — 00: 42
a. Group/COTP Command and Control ................ 42
(1) Communicate on Assigned Channels. ........... 43
(2) Communicate to All of Group AOR. ........... 43
(3) Communicate Using Secure Means ............ 45
b UR COo vv ili ei A TA ka a po 45
23251 uu el meat esci dae ee, Weer aye en 46
нә “Dee odda limi ə əə: 46
b. Geographical Display Operational Computer ........... 47
qını cio naa a 2757 de 48
B. NDS PUBLIC COMMUNICATIONS REQUIREMENTS ......... 49
IAE tapi hedi Requirements s uaar ea əl 49
ae aPieHalgSelective Calline Ла AA e 49
0557510303 NM 8 car E 51
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NA II C hannel Selectabilty A 1 53
e. VHF-FM Radio Direction Finding ................. 54
V11
2. Potential AI G bp RD O M 56
a. Differential Global Positioning System Transmissions .... 56
b. “VIS/MARDEZ interface (secure) ә ии мн 57
c. Dependent Surveillance ..... . > O i 57
V. EVALUATION OF SELECTED TESHNOEOGY A ин 59
A. RADIO DIRECTION FINDING 7 59
1. Discrete Systems on METEO... n nn 61
2. Integrated Systems AA TTE 62
B. VHF-FM IRANSCEIVERS 1, £C?7? ии 67
1. Chamel Selectivity "daaa 6 ии 68
2. Eneryption ......-. CERDOS c 69
3. Digital Selective Callingi5 5627 IN 70
C. RADIO PACKET SWITCHED NETWORKS ................. 72
1. ALOHA Netvorko...... ii enn TS
2. Graphical Analysis, Archiving and Display Station .......... 74
3. High Frequency Data link(HEDEE $ 0”. 7
4. Amateur Radio Packet Switched Networks (AX.25).......... 80
VI. SUMMARY AND RECOMMENDATIONS ...................... 82
A. FUNCTIONAL MODEL Ns | 82
B. SYSTEM CAPABIPEPIESERR A ә n 89
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RETO LO e Installation n as na n 95
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APPENDIX A ................. R. p ии 101
APPENDIX B ossaa nae eane nn DS sss 700. 103
APPENDIX C nunaa Si o AA AA"... уӱуУ— 157
APPENDIX D”... Snn e 73007 CT 162
APPENDIX E . wee. ..9.. ri x 164
INITIAL DISTRIBUTION LIST A ии 166
LIST OF FIGURES
Figure 1 Coast Guard Command and Control Structure ................... 7
Figure 2 Coast Guard Headquarters OrcanZallon a. Ka NA BE RIS 19
Figure 3 Coast Guard Area Staff Organization ....... .................. 20
Figure 4 Coast Guard District Staff Organization... ER 21
Ligure 5 National Distress System Configuration a E 35
Figure 6 Group Miami Representative RDF Display .................... 41
[cure 7 Ivpicalilniosraticd RDE' Display a bet as 64
Figure 8 High Frequency Data Link Configuration ..................... 78
Figure 9 NDS Radio Frequency Information Flows ..................... 84
MATE O NDS Remote Site Configuration Ian a e edo etl ды 85
Figure 11 NDS COMMCEN/OPCEN Configuration .................... 87
XI
I. INTRODUCTION
A. BACKGROUND
Approximately 20 years ago the United States Coast Guard established a nctwork
of coastal and inland Very High Frequency-Frequency Modulated (VHF-FM) transceiver
sites for the purpose of monitoring the National VHF-FM Maritime Distress Frequency,
156.8 Mhz, CH 16. This network was originally called the "National VHF-FM Radio-
telephone Safety and Distress System,” later shortened to the "National VHF-FM Distress
System" (NDS), and now commonly referred to as the "high sites." This system was
installed to:
..provide distress, safety, and command and control VHF-FM communications
coverage... in all areas of boating activity (including inland waters) in which the
Coast Guard has SAR responsibilities... [Ref. 1:p. 1]
This NDS has served the Coast Guard well over the past 20 years for Search and
Rescue (SAR), internal command and control (C?) and interaction with the boating
public. However, the increase in the number of VHF-FM "marine band" channels used
by the public, the improvements in VHF-FM technology, and the aged condition of the
original equipment has resulted in the need to replace the current outdated hardware with
"state of the art" technology.
In addition to the improvements in technology, there have been increased require-
ments placed upon the Coast Guard and the VHF-FM communications system. The ini-
tiation of the Digital Selective Calling (DSC) standard, a demand for Radio Direction
Finding (RDF), the concept of dependent surveillance, and the need for using secure
internal communications for Coast Guard C” have all vvorked together to precipitate the
NDS replacement project or "recapitalization."
B. RESEARCH OBJECTIVE
The purpose of this research is fourfold. First, to examine the original purpose and
configuration of the NDS. Second, to identify both the established and potential addi-
tional requirements placed upon the NDS since its inception. Third, to investigate and
summarize the technology that is applicable for fulfilling those new requirements.
Finally, to make conclusions and recommendations regarding the configuration and capa-
bilities of the new system.
C. RESEARCH APPROACH
The research portion of this thesis includes a literature search, a review of Coast
Guard directives and policy regarding the NDS, collection of information from Coast
Guard Engineers and Project Managers regarding current Coast Guard initiatives, and a
survey of available technology. This survey will include obtaining manufacturers'
information and specifications regarding equipment currently in production or planned for
production.
D. IMPORTANCE TO THE COAST GUARD
This thesis will represent a complete analysis of the present NDS, the new
requirements placed upon it, and the applicable technology available to fulfill those
requirements. The NDS is a vital communications system, and as such supports a large
part of the Coast Guard's C^, especially at the Group/Air Station/Captain of the Port level
and below. (The term Group will be used throughout this thesis but will generally mean
all three). Need for increased utility of the system, coupled with a more restrictive budget
climate, mandates that the replacement of the NDS be performed in the most cost-effec-
tive manner while still fulfilling the requirements of the system.
Current Coast Guard initiatives in several areas may have an influence on the NDS
upgrade. These initiatives include (but are not limited to) the Differential Global
Positioning System (dGPS), the Vessel Traffic Service (VTS), Radio Direction Finding
(RDF), Digital Selective Calling (DSC), Geographical Display Operations Computer
(GDOC), the Hybrid Data Network (HDN), the Secure Data Network System (SDNS),
and the Remote Data Satellite System (RDSS). The managers of these projects have an
interest in the NDS recapitalization and must be able to provide input prior to the
finalization of the system specifications. Lack of participation by all users or potential
users of the NDS could lead to the design and installation of a system that would not
effectively fulfill the needs of those users.
E. THESIS OUTLINE
1. Chapter II: Present Coast Guard C? Structure and Missions
In Chapter I the author will review the current Coast Guard missions and the
administrative and operational C* structure used to support the execution of those
missions. The author will provide a basic concept of the command and control structure
that depends on the NDS to provide communications to Operational units, and the
important role that the Program Managers play in the command and control structure.
2. Chapter III: National VHF-FM Distress System Background
Chapter III contains an overview of the present NDS and related VHF-FM
installations including:
e History of the NDS.
e Current statutory requirements placed upon the NDS.
e Current NDS configuration.
ə Other Non-NDS local-use VHF-FM installations.
3. Chapter IV: Established and Potential NDS Operational Requirements
Chapter IV details requirements that the NDS upgrade will need to address.
These are the additional requirements that have been placed upon the system since its
original installation. “These requirements are separated into two groups, those that have
already been established for the new system and those that have the potential to be placed
upon the system. These are addressed in two general areas: internal Coast Guard
communications requirements, and NDS public interaction requirements.
4. Chapter V: Evaluation of Selected Technology
Chapter VI investigates and describes the emergent technologies that would
enable the NDS to fulfill both its established and potential requirements. In this
investigation the author will discuss currently available systems that can fulfill
requirements similar to those outlined in Chapter IV.
5. Chapter VI: Summary and Recommendations
Chapter VI provides recommendations as to which technologies should be used
to fulfill the established and potential requirements of the NDS and the steps necessary
to implement the recapitalization. The author will provide these recommendations in
generic terms in order to not prejudice them towards or away from any one manufacturer
Or system.
II. PRESENT COAST GUARD C” STRUCTURE AND MISSIONS
A. COAST GUARD C” STRUCTURE
In order to comprehend how the VHF-FM National Distress System is used, it is
essential to appreciate the scope and missions of the Coast Guard, and the Program
Managers who administer those missions. It is especially important that the reader
understand the Coast Guard's Command and Control (C2) structure. In this chapter, the
author explains the Coast Guard's C* structure, its missions, and the applicable Program
Managers.
1. Coast Guard Command and Control Structure
The Coast Guard's Command and Control structure is shown in Figure 1.
General tasking for mission execution is set forth in regulations and directives created at
the Headquarters level. More specific tasking is provided by the Commanders at each
subordinate level, with the units' direct superiors in the chain of command assigned the
responsibility for developing specific operational orders for the units under their control.
At each level the commanders are aided by their staffs, who carry out the commanders'
orders in the day-to-day operation of that command.
The Command and Control structure is flexible, and can be changed as a
result of mission needs or specific events. For example, a vessel will depart its home
District or home Group and voyage to another Group or District to carry out its orders.
When the vessel arrives at the location where it will be working, it Changes Operational
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Figure l Coast Guard Command and Control Structure
Control (CHOP) to the new region, and works for the appropriate superior in the execu-
tion Of its missions until finished, and then retums to its home and CHOPs back to its
original command.
2. Coast Guard Communications Structure
The communications structure in the Coast Guard can be divided into two
broad areas. The first is tactical communications. The Coast Guard's primary tactical
short range communications system is the National VHF-FM Distress System. VHF-FM
is the communications medium of choice for mobile short-range communications. It is
used for communications between shoreside Marine Safety Offices and crews dispatched
in vehicles. It is also used for communications between cutters at sea and their
dispatched boarding teams and boat crews. It is usually the only communications link
between a Group/COTP or station and their underway vessels. It is also used, along with
UHF equipment, for communications between aircraft and cutters or between aircraft and
Groups.
The second communications area is that of long range communications. There
are five major systems, those of terrestrial record message traffic, terrestrial data and
electronic mall traffic, terrestrial voice traffic, ship-shore/shore-ship message and voice
traffic, and the radio navigation control system.
The terrestrial record message traffic system consists of micro-computer--
based terminals connected via leased lines to centralized message processing centers
located at the District Offices, Areas and Headquarters. This network interconnects with
the DOD AUTODIN network at the District level, and provides connectivity with the
DOD and other Government agencies. A second part of the terrestrial network is the
Secure Command and Control Network (SCN), which provides secure teletype services
to the Districts, Headquarters, and the Coast Guard Communications Stations. A second,
limited shore-side secure message transmission capability has recently been developed
using Secure Telephone Units (STU-III) connected to facsimile machines, now upgraded
to terminals connected to each other via dial-up STU III data units.
The terrestrial data and electronic mail service is named the Hybrid Data
Network (HDN). The HDN is comprised of a combination of dial-up and dedicated lines
connecting the Coast Guard Standard Workstations with the SprintNet X.25 packet
switching network. The HDN permits the transmission of data from individual units to
Other units or to mainframe computers.
The primary terrestrial voice communications network used is the Federal
Telephone Service. In order to enable secure voice communications over FTS, units use
STU III's. A second, smaller terrestrial phone system is the Search and Rescue Telephone
(SARTEL) network, which provides dedicated connectivity between Group Offices,
District Operations Centers, and associated command centers from other agencies involved
in Search and Rescue. The Coast Guard also has limited access to the DOD's Automatic
Voice Network (AUTOVON), usually at District, Area and HQ Operations Centers and
at Communications Stations.
Ship-shore and shore-ship traffic, both message and voice, is generally
handled through high frequency (HF) systems. “The Coast Guard operates Com-
munications Stations (COMMSTA) which provide the interface between the terrestrial
networks and thc deployed vessels. The Coast Guard uses both secure and non-secure
HF teletype communications, and has developed a polled, packet-switched data link
called the High Frequency Data Link (HFDL) for secure record traffic communications.
Secure ship-shore/shore-ship voice traffic uses both Parkhill and Vinson equipment over
HF radios. Somc of the larger cutters are equipped with DOD- provided satellite commu-
nications cquipment, and therefore can receive the Navy Fleet Broadcasts and messages
via the Naval Communications Processing and Routing System (NAVCOMPARS) and
Naval Communications Stations.
B. COAST GUARD MISSIONS
The Coast Guard has acquired many varied missions throughout its 200 year history.
Although these missions can be separated into rather distinct areas, the very nature and
size of the Coast Guard mandates that most units be "multi-missioned," i.c., able to carry
Out more than one specific task. As a result, a floating unit underway may be enforcing
laws One minute, conducting search and rescue literally the next minute, and then later
the same day be performing an aids-to-navigation mission. However, the responsibility
for the management of the various missions are given to the separate "Program
Managers," and it is by this separation that the missions arc classified.
1. Search and Rescue
The Coast Guard is probably best knovvn for their activities involving Search
and Rescue (SAR). The Coast Guard has been tasked by the National SAR Plan with
conducting Maritime SAR, which includes search planning and execution along the
10
coasts, in Hawali, Guam, Alaska, and Puerto Rico, as well as on the Great Lakes and
internal U.S. waterways.
The key component of the SAR mission within 30 miles of the coasts are the
156 Coast Guard Stations and 12 Search and Rescue Detachments (SARDET). These
stations and SARDETs, crewed with 10 to 45 people and equipped with versatile
multi-missioned boats, form the primary link with the boating public. Handling the SAR
responsibilities farther offshore are the more than 80 patrol boats, ranging from 82' to 110
long. These cutters are used to rescue or tow larger vessels and to patrol offshore for
several days at a time. Short range helicopters are also used close inshore for SAR,
longer-range helicopters perform missions as far out as 200 miles. Out on the open sea,
long-range fixed-wing aircraft and large cutters manage the SAR mission. The Coast
Guard also maintains communications stations to monitor distress calls on VHF- FM, HF,
and MF frequencies. The Program Manager for SAR is the Search and Rescue Division,
Office of Navigation Safety and Waterway Services at Coast Guard Headquarters.
4. Maritime Law Enforcement
Although SAR has been the most visible mission of the Coast Guard, the
service's very Origins were in Maritime Law Enforcement (MLE). The Coast Guard
began as the "Revenue-Marine Service" in 1790 to put a halt to the smuggling of goods
into the fledgling United States. Since that time, the MLE mission has grown to include
enforcement of all applicable laws and treaties in the navigable waters of the United
States and aboard U.S. flag vessels on the high seas.
L
Currently the MLE mission involves enforcement of Federal regulations
relating to the Continental Shelf and the Exclusive Economic Zone of the U.S., and other
territory or possession of the U.S.. Historically all Coast Guard cutters have been tasked
with law enforcement duties. To carry out its MLE mission now the Coast Guard has
added E2-C "Hawkeye" planes -- AWACS-type aircraft used to track drug smuggling
aircraft, Fast Coastal interceptors (FCI) -- Cigarette-type speedboats to chase them, and
Aerostats -- balloon-carried radars used to track drug smuggling vessels. Recently the
Coast Guard has also employed small Law Enforcement Detachments (LEDET) as
boarding teams embarked upon Naval vessels to combine the advanced sensors and
intelligence capabilities of those vessels with the law enforcement power of the LEDET.
The Program Manager for MLE is the Law Enforcement Division, Office of Law
Enforcement and Defense Operations at Coast Guard Headquarters.
3. | Recreational Boating Safety
The Coast Guard's mission of Recreational Boating Safety (RBS) exists to
reduce the risk of injury, property damage or loss of life associated with the use of
recreational boats in the U.S.. The RBS program involves certification of vessels, life
jackets, and safety devices for the boaters. It also involves the efforts of the Coast Guard
Auxiliary who volunteer their time and facilities, including vessels, to conduct boating
safety classes and Courtesy Marine Examinations (CME). Station personnel are
frequently involved in RBS as part of their SAR and MLE missions. The Program
Manager for RBS is the Boating Safety Division, Office of Navigation Safety and
Waterway Services at Coast Guard Headquarters.
12
4. Ice Operations
The Ice Operations mission for the Coast Guard began with the an Executive
Order in 1936 which established a national policy of using vessels for icebreaking duties
in U.S. channels, rivers, and harbors. Presently domestic icebreaking is carried out by
140 ft and 65 ft icebreaking tugs, which maintain ice-free channels on the Great Lakes
and the Atlantic Coast. Also breaking ice on the Great Lakes is the 290 ft USCGC
MACKINAW (WAGB 83). The polar icebreaking duties are shared by the 399 ft
USCGC POLAR SEA (WAGB 11) and USCGC POLAR STAR (WAGB 10). The
Program Manager for ice breaking is the Ice Operations Division, Office of Law
Enforcement and Defense Operations at Coast Guard Headquarters.
5. Waterways Management
The objective of the Waterways Management (WWM) mission is to develop
and implement traffic management techniques and navigation safety procedures for U.S.
ports and waterways. These include both passive techniques such as navigation regu-
lations and rules, and active programs like Vessel Traffic Services (VTS). There are
VTSs established presently in six harbors in the U.S., they provide traffic management
using VHF-FM radio, radar, and closed-circuit video cameras to collect, evaluate,
coordinate and disseminate information on vessel movements to other vessels.
Another part of the WWM mission is that of Bridge Administration. The
Coast Guard has responsibility for approving the location and plans of bridges and
causeways constructed across navigable waterways in the U.S.. The Coast Guard is
responsible for enforcing regulations concerning lighting for navigation, structure
15
modifications, and temporary obstructions for over 18,000 bridges in the U.S.. The
Program Manager for WWM is the Office of Navigation Safety and Waterway Services,
CG Headquarters.
6. Aids to Navigation
The Aids to Navigation (ATON) mission actually predates the MLE mission
by one year. In 1789 the Lighthouse Service was started, at that time the Federal
Government took over the maintenance of lighthouses from the individual states. The
Lighthouse Service became part of the Coast Guard in 1939. Presently the mission of
ATON is divided into two major areas. These are:
a. Short Range ATON
Short range aids to navigation are lighthouses, buoys, daymarks, fog
signals and ranges. Present-day lighthouses are no longer manned, the status of the light,
generators, and associated signalling devices is tracked by the Automated Control and
Monitoring System (ACMS) equipment and transmitted back to a Group office.
Short-range aids to navigation are maintained by over 80 buoy tenders, from 65 ft to 180
ft, and the 65 Aids to Navigation Teams (ANT) located throughout the U.S., which use
smaller buoy tenders from 18 ft to 47 ft.
b. Long Range ATON
Long range aids to navigation all use some form of radio-navigation.
Shore- based radio-beacons were the first radio-navigation aids established, now about
200 shore-based radio-beacons transmit a medium frequency "homing" signal out as far
14
as 50 miles. Later came the Long Range Navigation (LORAN) network, LORAN-A,
which was used in World War II. Nowadays 42 LORAN stations, 38 manned by Coast
Guard personnel, comprise the current low frequency Loran-C network. This network
provides one-quarter mile navigational accuracy for vessels and aircraft worldwide in
selected areas of the Northern hemisphere. The navigational system called Omega was
developed to provide global oceanic navigational coverage. Omega uses very low
frequency radio waves to provide four-mile accuracy. There are currently eight Omega
stations, two manned by the Coast Guard, the other six manned by the host countries.
The Coast Guard also publishes the Notice to Mariners and broadcasts the
Broadcast Notice to Mariners, both vehicles used to inform mariners of changes in
channels, channel markings, obstructions, or other issues of marine safety and navigation
within the local areas. The Program Manager for ATON is the Office of Navigation
Safety and Waterway Services at Coast Guard Headquarters.
7. Marine Environmental Response
The Coast Guard's mission of Marine Environmental Response (MER) exists
to minimize the pollution damage and reduce the threat of potential pollution through
planning and response. The Coast Guard maintains the National Response Center (NRC)
in Washington, DC. The NRC acts as a centralized reporting point for spills of oil or
hazardous substances in U.S. waters, and coordinates the cleanup of spills when they oc-
cur. Management and operation of the MER mission at the unit level is carried out by
the 42 Marine Safety Offices (MSO), four Captains of the Port (COTP) and 17 Marine
Safety Detachments (MSD) located in the major ports of the U.S.. They patrol the
15
harbors and shoreside facilities using cutters and boats from 12 ft up to 110 ft and
numerous vehicles. The Commanding Officer of the MSO also acts as the COTP for that
location.
The MER also includes the mission of Marine Science Activities (MSA).
MSA operates the International Ice Patrol to track icebergs, the data buoy profect to
provide weather reporting buoys for offshore locations, and the weather observation
project to provide weather observations from selected cutters and stations directly to the
National Weather Service. The Program Manager for MER is the Office of Marine
Safety, Security and Environmental Protection at CG Headquarters.
8. Port Safety and Security
The Port Safety and Security (PSS) program involves three elements, port
safety, port security, and environmental protection. As a result of the similarities with
the MER program, the two are usually conducted by the same units, the MSO's, MSD's,
and COTP's. The primary activities of the PSS include the monitoring of oil or hazardous
cargo transfer Operations to prevent spills, the inspection of vessels to ensure compliance
with Federal regulations, the examination of waterfront facilities to prevent fires,
explosions or other accidents, safeguarding vessels and port areas from sabotage or
terrorism, responding to maritime emergencies or natural disasters affecting the ports of
the U.S., and preparing for mobilization, including handling of hazardous cargos and pro-
viding land-side and waterside port security. The Program Manager for Port Security is
the Office of Readiness and Reserve, Coast Guard Headquarters.
16
9. Commercial Vessel Safety
The mission of Commercial Vessel Safety (CVS) includes the missions of
Marine Inspection and Marine Licensing. Marine Licensing involves the licensing and
certification of U.S. Merchant Marine Officers and Scamen. This is administered at 17
Regional Examining Centers nationwide. Marine Inspection includes the inspection of
U.S. flag vessels from design to decommissioning. Inspection is carried out by a team
from an MSO, Marine Inspection Offices (MIO), COTP, or MSD. The Program Manager
for MER is the Office of Marine Safety, Security and Environmental Protection at CG
Headquarters.
10. Defense Operations
In accordance with 14 USC 2 and 14 USC 145, the Coast Guard has the
responsibility to act as an armed Naval force. Toward that end the Defense Operations
(DO) mission has been established. Included in the mission is military readiness, small
arms training, and weapons system proficiency. The Coast Guard is also responsible for
the maintaining the Maritime Defense Zones (MDZ) for coastal warfare, defense planning,
and exercises. In war, or when the MDZs are activated, the Coast Guard MDZ
commanders have responsibility for port security and coastal defensive operations within
200 miles offshore. The Program Manger for DO is the Office of Law Enforcement and
Defense Operations at Coast Guard Headquarters.
17
C. COAST GUARD PROGRAM MANAGER MISSION SUPPORT
Within each Headquarters Office are the Program Managers, who manage the
missions and programs. Program Managers make decisions regarding the planning,
funding and execution of the programs, and provide mission support to the subordinate
units. They work through their counterparts on the Area or District staffs in dealing with
the units for which they are responsible. The Program Managers at each level are usually
not specific individuals, but are the members of the staff elements assigned to the division
or branch that manages the program. The organizational structure of Coast Guard Head-
quarters is shown in Figure 2.
Area Staffs have some Program Manager counterparts, however Areas are not
heavily staffed and therefore do not have Program Managers for all the missions. A
representative Area organization is shown in Figure 3.
District Staffs have Program Managers for each of the programs being carried out
within their district. A typical District staff organization is shown in Figure 4.
As it can be seen, the various staff elements and organizational levels create a
complex interconnecting network, which is dependent upon the C? structure of the Coast
Guard to manage the missions assigned. In general, the vision of the Program Managers
in regards to C? issues is focused upon the administration and execution of their specific
missions. As a result, systems which serve several missions must be able to fulfill the
requirements for each of those missions without adversely affecting other missions. Any
project which changes the C° structure must be sensitive to the needs and demands of the
various mission areas, and be formulated accordingly.
18
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HI. NATIONAL VHF-FM DISTRESS SYSTEM BACKGROUND
In this section the author details the origins of the National Distress System (NDS)
and its present configuration. Included are descriptions of related VHF-FM systems that
are in use as part of the Coast Guard's C? communications, but not currently part of the
NDS.
A. HISTORY OF THE NDS
The material for sections 1 and 2 below, the history of the NDS and the actions that
caused its formation, has been drawn collectively from References 2, 3, and 4.
1. Creation of Network
The Coast Guard has the statutory responsibility for the:
... development and operation of rescue facilities for the promotion of safety
on and over the high seas and waters subject to the jurisdiction of the United
States. [Ref. 5]
As a result, the Coast Guard's communications systems must be capable of
handling both internal Coast Guard traffic and external traffic between the Coast Guard
and the mariner.
Creation of the NDS was a long and involved process, beginning shortly after
World War II. The first step was the designation of the frequency 156.8 MHz in 1946
as the international frequency for distress and calling. Once this designation was made,
the United States began vvork to carve out a maritime mobile band somevvhere around this
156.8 MHz frequency. Prior to 1948, there were two separate bands, 152-162 MHz for
non-Government radio services and 162-174 MHz for Government radio services. This
separation of Government and non-Government frequencies was worthwhile to most
agencies, but it proved a hinderance to the Coast Guard. The Coast Guard needed a
frequency band for communications with the public in the 152-162 MHz range, and was
willing to surrender frequency allocations within the 162-174 MHz range in trade. In
1948 the Interdepartment Radio Advisory Committee (IRAC) and the Coast Guard agreed
that the sub-band at 157.050-157.25 MHz, later specified to be Channel 22A at 157.10
MHz, would be used for safety purposes for government-nongovernment liaison
communications. This initiated the marine VHF-FM band for use between the Coast
Guard and the mariner, and eventually resulted in the creation of the NDS to use that
band.
Since that time the Coast Guard has been committed to development and use
of a VHF-FM radiotelephone network for short-range maritime distress and safety
communications. At first, progress in creating that network was stalled due to low public
acceptance of VHF-FM as the mariner's medium of choice. It was a classic "chicken-
or-egg" dilemma--the mariners would not purchase VHF-FM equipment unless they
could use it to talk to the Coast Guard, and the Coast Guard would not fully invest in the
network unless there were marine radios in common use. The Coast Guard finally started
implementation of the network when the Federal Communications Commission (FCC) and
IRAC expanded the versatility of the system by permitting the Coast Guard to use
VHF-FM for short-ranged command and control communications in addition to distress
and safety traffic. Once that decision had bcen made, the Coast Guard started to establish
the NDS network in earnest.
Three specific actions then increased the mandate for using VHF-FM marine
radios onboard vessels. First, in 1968 the FCC and IRAC designated 156.8 MHZ
(Channel 16) as the National Maritime Distress Frequency. Prior to that time Channel
16 had the designation of being a safety frequency, but not a distress frequency within
the United States, although it had been internationally both a safety and distress frequency
since 1946. Second, Congress passed the Vessel Bridge-to-Bridge Radiotelephone Act
in 1971. This act required that the masters of certain commercial, salvage and passenger
vessels monitor the designated channels within the VHF-FM marine band (156 MHz -
162 MHz) while underway. Channel 13, 156.65 MHz, was selected to be the designated
bridge-to-bridge channel. Third, in 1972, the FCC solidified the use of VHF-FM as the
primary short-range maritime communications system by limiting the issuance of single
sideband (SSB) licenses to vessels. Until that time, boaters had used double sideband
(DSB) radios in the 2 MHz band for communications. The FCC action forbade the use
of these DSB radios completely and prohibited installation of SSB radios unless the vessel
already had a VHF-FM marine band radio installed and the vessel's owner could show
a need for the SSB radio. These three factors increased the pressure upon the Coast
Guard to establish their VHF-FM network.
24
In order to prepare for the full conversion to VHF-FM, the Coast Guard
started a project in the fall of 1970 to develop the National VHF-FM Radiotelephone
Safety and Distress System, as originally named. The project objectives were:
è Define the Coast Guard's policy, both short and long term with regard to VHF-FM
coverage, facilities, and services.
e Present a comprehensive survey of existing facilities, requirements, and needs.
e Forecast the future operational requirements of the Coast Guard with considerations
of SAR coverage, boating trends, legal restrictions, international treaties, requests
of other government agencies both federal and local and operational capabilities.
[Ref. 4:p. 3]
As a result of the project, the communications requirements of the system
were determined to be:
e Coastal area coverage must be provided to at least 20 miles offshore, and in
adjacent tidal waters. In areas where heavy concentrations of boating activity exist
greater than 20 miles offshore, coverage will also be provided to the extent
practicable;
e Complete coverage of all large bodies of inland water such as Puget Sound, Long
Island Sound, Chesapeake Bay and the U. S. waters of the Great Lakes is
necessary;
e Coverage of the navigable waterways where commercial or recreational traffic exists
and the Coast Guard has SAR responsibility;
€ Provide improved VHF-FM coverage in coastal areas of Alaska and Hawaii to the
extent it is feasible considering the geographical characteristics of these areas. [Ref
3:p. 3]
The system was planned to provide this extensive coverage economically
through the use of remotely controlled, relatively high-elevation antenna sites, thus the
unofficial name of "High Site System.” Concentration was On maintaining a high state
of readiness and optimizing the receiving capability. The assumption was made that
transmissions from mariners to the antenna high site locations would be made from
transmitters operating at one watt of power with a half-wave dipole antenna at sea level.
This ensured that even weak transmissions would be detectable within the design
parameters of 20 miles offshore. The original design criteria for the system is provided
in Appendix A, Original National Distress System Design Criteria.
2. Initial NDS Installation
Prior to the installation of any new system, a survey of the existing Coast
Guard VHF-FM installations was made. This survey showed a variety of antenna
heights, receiver sensitivities, and effective ranges for the installed systems, most
unsuitable for use with the NDS. Plans were then made to standardize these installations
and incorporate them into the NDS. Upon completion of the final plan, site locations
were finalized and equipment was ordered. The transceiver had six channels which could
be remotely controlled from another unit called the remote control unit (RCU). Selection
of the channels was made using in-band signalling via 15 audio control tones. The first
site became operational in the fall of 1971, and shortly afterwards another 40 sites were
installed and operating. These early sites provided radio coverage for Long Island Sound,
Chesapeake Bay, the coasts of Maine, Florida, North Carolina, most of the Gulf Coast,
selected areas of the Great Lakes, the Northern California coast, and Puget Sound.
26
Some of the more remote sites lacked telephone service and had to be linked
vla a duplex UHF circuit for the transceiver signal and control functions and a VHF
repeater for the channel 16 guard receiver. Other sites were linked via Coast Guard--
owned, shared or leased microwave systems. Most of the routine installations were able
to be remotely controlled from more than one RCU, giving the operators flexibility and
multiple access to the individual sites. Customarily both the Group COMMCEN and the
nearest small-boat station had control over the local NDS transceiver, permitting control
and use by either.
A second phase of 40 more sites was ordered for July 1973 and a third phase
of 40 more sites was scheduled for the following December, subject to budget restrictions.
Most of these were eventually installed.
Since the initial installation there have been numerous changes made as
empirical data located geographical areas that were not covered by the NDS. Many of
these VHF-FM "holes" have since been corrected, but the research regarding VHF-FM
coverage and the modification of the system continues. The present configuration of the
NDS is contained in Appendix B, National Distress System Transceiver Location
Information.
B. NDS STATUTORY REQUIREMENTS
As indicated above, the Coast Guard has the statutory responsibility for the
... development and operation of rescue facilities for the promotion of safety on
and over the high seas and waters subject to the jurisdiction of the United States.
[Ref. 5]
Included in the operation of those rescue facilities is the need for communications,
both between the Coast Guard and the public and within the Coast Guard. The VHF-FM
NDS network exists to provide those communications on a short-range basis.
1. VHF-FM Channel 16 Monitoring
The Coast Guard's responsibility for monitoring the VHF-FM Distress
Frequency, Channel 16 (156.8 MHz) is based upon international agreements and federal
regulations. The United States is a member of the International Telecommunications
Union (ITU), and therefore adheres to its obligations as a member. The ITU states:
The frequency 156.8 MHz is the international distress, safety and calling frequency
for radiotelephony for stations of the maritime mobile service when they use the
frequencies in the authorized bands between 156 MHz and 174 MHz... It is used
for the distress signal, the distress call, and distress traffic, as well as for the
urgency signal, urgency traffic and the safety signal.. Safety messages shall be
transmitted where practicable on a working frequency after a preliminary
announcement on 156.8 MHz. The class for the emission to be used for radiotele—
phony on the frequency 156.8 MHz shall be G3E. [Ref. 6:Sec. 10.(1)]
In addition to the designation of 156.8 MHz as the VHF-FM distress, safety
and calling frequency, the ITU requires that all vessels maintain a watch on CH 16 for
distress traffic. The ITU states that
28
.. Ship stations should, where practicable, maintain watch on 156.8 MHz when
within the service area of a coast station providing international maritime mobile
radiotelephone service in the band 156-174 MHz. [Ref. 6:Sec. 87.(3)]
The Coast Guard Telecommunications Manual (TCM), which provides
guidance for telecommunications matters, indicates
The Coast Guard will provide a comprehensive distress telecommunications system
along the coast and on large inland waters of the United States and its possessions.
[Ref 7:Sec. 2.B.3.m]
Additionally, the TCM requires that
Area and District Commanders shall organize the communications facilities in their
area of responsibility and provide:
... Maintenance of continuous radio watches on the distress frequencies by as many
units as necessary to provide adequate coverage. All activities shall be alert to
intercept distress messages and relay them to the appropriate Operations center...
[Ref. 7:Art. 15.A.4]
and
Each Group Commander shall have a COMMCEN to serve as the focal point of all
communications activities within the Group... Continuous guards of the distress
frequencies 2183.4 (2182) kHz and/or VHF-FM Channel 16 are required...
VHF-FM working frequencies should be guarded when units are underway to
minimize calling on Channel 16... [Ref. 7:Art. 7.G.1]
The Coast Guard Telecommunications Plan (TCP) provides more guidelines
regarding the NDS by stating:
The National VHF-FM Distress System, operated on the maritime mobile band
( 156 MHz) by the Coast Guard, is designed to provide distress calling, maritime
safety information broadcast, and command and control coverage out to 20 nautical
miles (NM) offshore. Guard receivers for channel 16 (156.8 MHz) and mul-
ti-channel transceivers are normally operated by group commanders. Vessels and
aircraft guard channel 16 and are equipped with a transceiver. [Ref 8:Sec.
4.B.1.b.(3)(a)]
2. Internal Command and Control
As indicated above, the Coast Guard was given permission by the FCC and
IRAC to use the NDS for internal command and control. In addition to international
directives, the Coast Guard has established its own guidelines for the use of the NDS and
VHF-FM Marine Band transmissions. The TCM guidelines regarding communications
in general state that:
Operational Commanders shall have the capability to communicate rapidly with
operating units under their control. (Ref. 7:Art. 2.B.3.i]
The use of radios is specified as part of the Group C! system when the TCM
states that:
Group Commanders are each supported by an indigenous telecommunications center
which functions as the communications nodal point for all Group command, control,
30
and communications (C3) support activities. Connectivity with shorc units is
provided by landline and to mobile units by radio.... [Ref. 7:Art. 4.C.1.e]
This use of the VHF-FM NDS radio network for C^ has expanded over the
years to make the NDS system the primary C? system at the Group level for com-
municating with underway resources.
3. Public Safety Broadcasts
The Coast Guard is required to transmit Marine Information Broadcasts as part
of their marine safety mission. The TCM states:
The Coast Guard will maintain a capability to transmit Marine Information
Broadcasts (MIB) into its areas of responsibility in a form usable by the recipient.
[Ref. 7:Art. 2.B.3.k]
Group cOmmunications centers use the NDS to transmit scheduled Marine
Information Broadcasts four times a day and weather and Urgent Marine Broadcasts on
demand.
4. Public Communications
As an integral part of the SAR mission, it 1s necessary for the Coast Guard
to be able to communicate with vessels underway, for both the Marine Information
Broadcast and for general communications with the boating public. The TCM states:
41
The Coast Guard will maintain a capability to communicate directly with merchant
ships, fishing vessels and recreational boats. (Ref. 7:Art. 2.B.3.1]
This Coast Guard-to-public communications is also an integral part of the
Vessel Traffic System (VTS) mission. The vessels participating in the VTS itself are
required to maintain contact with the VTS Center via Channel 13 or any VHF-FM
channel designated by the VTS for its use. Many VTS's have sites in addition to the
NDS that they use for communicating directly with their participating vessels. The VTS
sites are contained in Appendix C, Vessel Traffic System Transceiver Location
Information.
C. CURRENT NDS CONFIGURATION
l. Architecture
Figure 5 shows a representative configuration for the NDS. In this example
the three transceiver sites have the ability to be controlled by either of two remote control
units (RCU). Primary control is usually at the Group COMMCEN, which maintains a
24-hr watch on CH 16 for the three sites. Secondary control is possible at the local
control sites. “These local control sites are usually at the Coast Guard stations that are
closest to the NDS transceiver locations. “This redundancy reduces the loss of
communications capability should the link between the transceiver site and the Group fail.
It also permits the station to use the NDS for command and control of their deployed
resources if their own low-power VHF-FM transceivers are unable to contact those
resources.
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33
2. Hardware
Because the installation of the hardware has occurred over a span of time,
there are several variations to the initial installation. As noted, there have also been
modifications made to the system as operational demands have been changed. Groups
have identified the need for additional coverage, or additional channel capacity, or even
the need for secure repeaters to handle the lower-power DES transmissions.
a. Transceivers
The transceivers, located at the antenna sites, are typically Motorola
6-channel base stations, assigned either the model number C53 RTB 3146 SP1 (MICOR)
or C53 MHB 1106 AR (MOTRAC). Either one provides up to 100 watts of output
power. Most installations have the output power adjusted to be 50 watts at the antenna.
Power to the transceivers is usually provided by the local electrical utilities, with only
some sites having installed standby generators available in case of power failure. In
Alaska, however, the sites are so isolated that special low-power transceivers using
electricity supplied by propane-gas fueled thermal electric generators are employed.
b. Remote Control Units
The original Remote Control Units (RCU) are Motorola Model
CGG-T-1616AM, which have the capacity to monitor the Channel 16 Guard Receiver
and also remotely control the 6-channel transceiver. Motorola updated the original RCUs
and newer equipment goes under the Motorola name of CENTRACOM, which has the
same capabilities but occupies less console space.
34
c. Antennas
As indicated in Appendix B, the majority of thc antenna installations arc
folded dipoles. The installations have been tailored, hovvever, to the local conditions such
that various other types of antennas have been used. “The reader should note the
directivity of the antennas, in most cases the highest antenna gain 1s directed towards the
nearest body of water and away from the adjacent shoreline. This increases the
probability of detecting vessels offshore but hinders communications to vehicles on shore
or operations that might occur right on the beach itself. Also, the altitude of the
antennas has an effect upon the antenna coverage. The Commander, Fourteenth District
has had to install a downwardtilting (3-degree) antenna at their highest antenna site in
order to not "overshoot" vessels that are close-in to the shore.
d. Control and Communications Circuits
The primary control and communications circuits consist of two twisted
pair telephone lines. Once line establishes the CH 16 Guard receiver circuit to the RCU
and the other pair functions as the tunable transceiver circuit connection, carrying audio
control signals toward and voice both toward and from the RCU. These lines can be
"conditioned" voice grade lines, but various problems have been noted if lines other than
"data-grade" are used for the circuit. In some installations the circuit between the
transceiver site and the RCU is established using a microwave transmission system.
35
3. Transceiver and Remote Control Locations
a. Equipment Locations
Appendix B, Current NDS Transceiver Locations, contains a summary of
the NDS locations, their control sites, antenna types, antenna heights and antenna gains.
Information was obtained from both the NTIA database and each individual Districts.
Discrepancies were resolved by the applicable District.
b. Geographical Coverage
The current geographical coverage by the NDS 1s not accurately known.
In the past, individual Districts and Groups have collected empirical data and prepared
reports regarding coverage "holes" in their areas of responsibility (AOR). The most
recent official study available, conducted by the National Telecommunications and
Information Administration NTIA, was performed in 1980 [Ref. 9]. The results of this
study show the predicted propagation for both a 1—watt transmitter with a 0dB gain
antenna located 6 ft above the water and a 25—watt transmitter with a 6dB gain antenna
located 15 ft above the water. Currently the Telecommunications Division of Com-
mander, Atlantic Area Maintenance and Logistic Command (MLC) is working to acquire
the software used by the NTIA in order that plotting can be done in-house. Once
available, this will enable the MLC to determine the theoretical coverage of NDS sites,
evaluate modifications, and provide the information to districts for their use.
36
4. System [ntegration
a. Connectivity Within the NDS Network
As indicated in Figure 5, the individual transceiver sites connect remotely
to primary and, in most cases, secondary RCUs. The multiple RCUs at the Group
Communications Center are usually connected in a way such that input from a single
microphone is fed to all of the transceivers controlled from that COMMCEN. This
enables the Radioman to perform his Marine Safety Broadcasts for the entire Group Area
of Operations (AOR) with one transmission. Besides the common microphone, there is
no other connection between individual transceiver sites or RCUs. There is limited
connectivity between primary and secondary control sites for the same NDS transceiver
site, however. The RCUS usually include an intercom feature which permits operators
at the primary and secondary sites to communicate between the two locations using a
simple push-to-talk intercom.
b. Connectivity With Other Networks
At this present time, there is little connectivity beyond the Group
COMMCEN/secondary RCU sites. As can be seen by the information provided regarding
primary and secondary remote control locations, some transceivers are remoted to both
the Group COMMCEN and another operations control center, usually an MSO or COTP.
Other than these additional remote control facilities, there is no connectivity between
transceiver sites from different COMMCENS, and only limited connectivity is provided
to any other outside network. In some installations the COMMCENS have a VHF-FM
37
telephone patch capability which enables a user to communicate over the NDS from a
remote location via the telephone system.
5.. Non-Standard/Special NDS Installations
a. Secure Communications
Due to increased pressures for secure communications during law
enforcement operations, there have been some upgrades made to the NDS to provide for
voice encryption. These upgrades include remote bases and repeaters. The repeaters are
used in the duplex mode in government frequencies above the marine VHF-FM band.
They are essential for operating when in the DES encrypted mode due to the lower trans-
mission power output in the DES mode. These installations have been done by the
Districts and are not part of the NDS system. Therefore, their existence is not reflected
in the information contained in Appendix B. The upgrade of the NDS, as indicated later
in this thesis, requires the inclusion of DES equipment, which will then likely incorporate
the capabilities of the secure communications equipment currently installed.
b. Data Channel Usage
In an effort to provide data communications to deployed vessels, several
locations in the Coast Guard have experimented with data communications via the NDS.
Systems have included radio packet-switched technology and simple transmission of
ASCII characters over a VHF-FM channel using standard 300bps audio frequency shift
keying (AFSK) modems. Presently only one system is in use, that of transmitting ASCII
using the AFSK modems over the NDS. [Ref. 10:p. 7]
38
c. VHF-FM Direction Finding Installations
At this time there are no VHF-FM radio direction finding (RDF)
capabilities using the NDS. There are no directional antennas, links to the Group
COMMCEN, or direction indicators installed. Commander, Pacific Area is working to
install a system that would use remote readout direction—-finding antennas installed at the
high sites in Hawaii for direction finding.
D. LOCAL USE VHF-FM SYSTEMS
1. Shore Unit Equipment
Standard shore-station VHF-FM equipment usually consists of a Motorola
MCX1000 DES encrypted radio. The MCX1000 mirrors the NDS equipment in that it
contains both a transceiver and a channel 16 "guard" receiver. The units therefore have
two speakers, one for just channel 16 and the other for the switchable transceiver. The
MCX1000 is capable of operating in the government frequencies above the VHF-FM
Marine Band, and is therefore compatible with DES radios used by the U. S. Customs and
Other government agencies. These radios are capable of transmitting 25 watts PEP in
normal voice Operations but are reduced to approximately 12 watts PEP when in
encrypted mode. Most shore unit local sites transmit through whip antennas having a 3dB
gain.
39
2. Shore Unit VHF-FM RDF Capabilities
a. Individual RDF sites
Many commands have provided various radio direction finding
capabilities for their shore units. The two primary manufacturers of RDF receivers used
are SIMRAD/TAIYO and Polaris. Each uses an Adcock antenna and a directional display
to indicate the direction of the received transmission. Neither make use of any capability
to capture the bearing data and manipulate it or transmit it on to a processor for further
analysis.
b. RDF Networks
There are currently two operational RDF networks in the Coast Guard,
both located in Florida. These non-NDS systems are identical in configuration, only
differing by the location. They each consist of three directional antenna locations which
send back the received audio and the direction bearing to remote speakers and an Apple
II computer respectively. The bearing information from the antennas is fed into the
computer, which processes it and provides: 1) the lines of position (LOP) from each
antenna site to the transmission source location, 2) a probability ellipse, within which
there is greater than a (typically) 9596 probability that the transmitter is located, and 3)
both the LOPs and the ellipse overlaid upon a chart of the RDF coverage area. A
representation of the RDF display for the installation at Coast Guard Group Miami is
shown as Figure 6.
40
——
3
MES-OE-6/0 :buon
N9C-76-6Z7 : 107
Си YO
—
O
Figure 6 Group Miami Representative RDF Display
41
IV. ESTABLISHED AND POTENTIAL NDS OPERATIONAL REQUIREMENTS
As indicated previously, the NDS serves as both the Coast Guard's primary
short-range command and control communications Circuit for deployed resources and the
public interface network on the VHF-FM marine band. As such, the NDS is fulfilling
certain statutory requirements, which were detailed in Chapter III. Recently there have
been initiatives which, 1f implemented, would place additional requirements on the current
NDS or its replacement. In this chapter the author analyzes the established and potential
operational requirements placed upon the NDS, separated into the areas of internal
communications requirements and CG-public communications requirements.
A. INTERNAL COAST GUARD NDS-RELATED REQUIREMENTS
l. Established Requirements
a. Group/COTP Command and Control
As noted previously, the NDS is a primary communications resource for
the Group/COTP Commander (called just Group here) to use in controlling his operational
resources. In order to do this, the NDS has to provide communications channels to and
from the Groups' operating units. The communications requirements fall under three
Specific categories: communication on the assigned channels; communication to all of
the Group Area of Responsibility (AOR); and communication via secure means.
(1) Communicate on Assigned Channels. An essential requirement of
the NDS in regards to the Group Operations Center (OPCEN) is that the Group has to be
able to communicate with its units on the assigned CG working frequencies. If the NDS
does not permit the Group to do that, then it is not fulfilling its C^ mission at the Group
level. The current NDS fulfills this requirement, although there are locations where there
are not enough working frequencies to prevent inter- or intra- Group interference. It also
does not permit communications with other agencies that use the government band above
162 MHz for secure communications. Specifically the DEA and Customs have
DES-capable radios that use the frequencies above 162 MHz for joint communications
with the CG over the Motorola MCX1000 radios. The present NDS sites, however, lack
DES capability at this time. It should be noted that the NDS may not be the most
effective method of Group C^ communications with its units. Other technology, such as
cellular telephones, may be a solution, but is outside the scope of this thesis.
(2) Communicate to All of Group AOR. Another essential criterion for
the NDS is that it enables the Group COMMCEN and OPCEN to communicate with its
deployed units within its entire geographical AOR. The current NDS is not configured
to completely fulfill this requirement. Numerous Groups and Districts have identified
locations or "holes" where VHF-FM NDS coverage is weak or altogether non-existent,
and work is being done to remedy the problems. References 11-14 are examples of this
effort. Until the problem is corrected, Groups will have to rely on secondary means (e.g.,
low sites) to maintain communications throughout their entire AOR's. It should be
obvious to the reader, but bears mentioning here, that this ability to communicate
43
throughout the Group's entire AOR mandates the use of either remote transceivers
controlled from a central location or an extensive network of repeaters.
A second issue is that Group or COTP AORS are not totally
coordinated with the NDS site locations. There are areas where the NDS site is
controlled by one Group but the area it covers is partially within another Group. Coor-
dination of operations is difficult in these situations. There are also instances of
MSOs/COTPs that do not have their own communications networks and must rely on the
NDS. In some of these areas, the MSO/COTP AOR stretches across several Group
AORs. Communications between the MSO/COTP must be handled through any of
several separate groups, depending upon the location of the underway unit. Access to all
the NDS sites covering the COTP's AOR is essential.
A third issue is that of communications with aircraft. Aircraft are
dispatched by CG air stations but are usually working for Groups in the execution of their
Operational missions. This requires that the Groups be able to communicate with the
aircraft to coordinate searches, pass information, etc. For most Groups the only
communications link with the aircraft is via the NDS using VHF-FM, which presently
functions well. At the same time, however, the air stations are attempting to maintain
communications with their deployed aircraft via UHF radio. The line-of-sight UHF
communications suffer from limited range, especially when the aircraft are Operating at
low (e.g., 500 ft) altitudes. The air stations need to remain in contact with their aircraft,
and therefore need access to the NDS, which most do not have.
+4
(3) Communicate Using Secure Means. A recent requirement of the
NDS is that it permit communications between the Group or Station and its resources via
secure means. Two directives, Presidential Directive 24 and National Security Director
Directive-145 require that all government internal communications be conducted over
secure circuits (Ref. 15, 16]. In the case of VHF-FM communications at the stations, this
has resulted in the installation of the aforementioned MCX1000 DES encrypted
transceivers on the vessels and at the station low sites. As of yet, the NDS has not been
officially upgraded to provide secure communications on a system-wide basis. Certain
districts have, however, provided their own upgrades in the form of encrypted base
stations and encrypted duplex repeaters to provide interim secure communications until
the NDS is brought to the secure level. Of all the districts, the Seventh has probably the
largest network of remote secure transceivers and repeaters to provide covered
communications throughout the southeast U. S.
b. Record Message Traffic
Related to the Group Command and Control issue is the requirement for
using the NDS to pass so-called record message traffic, i.e., written messages passed
either as data or voice over the NDS to and from deployed units. In the case of vessels
which lack teletype capabilities, the only method available for passing the traffic is using
voice over the NDS. The NDS is used to send messages from the deployed unit to the
nearest Group COMMCEN for further transmission over the Coast Guard's teletype
circuits. The NDS is also used by the same underway units for receipt of message traffic
45
from the Group COMMCEN s teletype netvvork. In both cases, the usual way of
transmitting the message is using voice which is a slow, labor intensive and error-prone
mcthod.
Several districts have experimented with using modems or packet radio
terminal node controllers (TNCSs) to automatically transmit the messages as data vice text,
with limited success [Ref. 10]. The Coast Guard's Information Systems Center conducted
a pilot project using amateur radio TNCs and MCX 1000 DES encrypted radios to
transmit data over VHF-FM channels. This Lovv Cost Packet/STTOR Communications
Profect found that data could be transmitted in covered mode at speeds up to 1200 baud
without error [Ref. 17:p. 13]. More information on recent research regarding the
VHF-FM system and data transmission is provided in Chapter V.
2. | Potential Requirements
a. Dedicated Data Channel
As indicated above, the NDS is currently used to pass record message
traffic using both just voice and data-over-voice channels. The need for certain vessels
to transmit and receive data while underway already exists, and the present solutions are
adequate but temporary. The need for an established separate data channel becomes more
and more evident as the matter is investigated.
Certain vessels have neither the manpower nor the equipment space to be
able to operate an HF radioteletype facility in order to transmit and receive messages.
None of the cutters on the Great Lakes or inland waters and most of the cutters 180' and
46
smaller are unable to send or receive administrative Or Operational record message traffic
while underway. Many of the new 110' cutters are equipped with High Frequency Data
Link (HFDL) equipment to overcome this limitation, but the older vessels are not
scheduled to receive HFDL equipment.
The establishment and use of a master law enforcement database for
boarding histories and violation information, Law Enforcement Information System (LEIS
II) encourages the need for a data link between afloat vessels and the shoreside networks,
especially the Hybrid Data Network (HDN). Long deployments of cutters coupled with
the mandated use of automated online procurement software drives the requirement that
vessels be in regular data communications with the shore. Creating a VHF-FM data
channel would enable this link without overloading the long-distance HF networks. This
data link could be used for two-way access to the teletype network, the ARMS service,
electronic mail, online LEIS II, and message traffic.
Use of the NDS for this data channel would enable communications from
shoreside mobile terminals to the network. This would permit CG members in vehicles,
onboard merchant vessels, or at emergency command posts to access the network using
laptop computers and the appropriate radio equipment.
b. Geographical Display Operational Computer
The Coast Guard's Electronics Engineering Center is Currently working
on a Geographical Display Operational Computer (GDOC) system, formerly known as the
Geographical Tactical Computer (GTC). This system, to be placed at cach Group
OPCEN, would serve as an electronic chart and database to provide positional and
47
facilities information within the Group's AOR. It is scheduled to also have search
planning and plotting features, as well as the ability to exchange data with other systems
[Ref. 18]. The GDOC would also be used to process RDF information from remote RDF
receivers, if available. If constructed as designed, it would have need for some sort of
data link between the NDS sites, Group resources and the GDOC in order to efficiently
pass information to and from underway resources and RDF receivers. There is also a
shipboard version of GDOC planned, called the Shipboard Command and Control System
(SCCS), which would have similar capabilities and would need data connectivity with
other units and the shoreside network.
c. NDS Network
As indicated in Chapter III, the current NDS is not a network, but a
system of independently-controlled transceivers remoted to Group offices. If the data
channel capability was added to the NDS, it would be necessary to connect all the NDS
sites together into a true network, and then provide connectivity between the NDS data
network and the other CG networks, probably via the Coast Guard's X.25 Hybrid Data
Network (HDN). Data would have to be routed dynamically from the network to the
closest data transceiver for transmission to the deployed unit.
The presence of an integrated VHF-FM direction-finding system would
require that the individual NDS sites were networked together, at least at the Group level,
in order to provide several lines of position and the resultant accurate RDF positional fix.
Logically Groups would also need to access adjacent Groups' sites in order to provide
satisfactory three—bearing RDF fixes.
48
The NDS' various users (Groups, MSOs, COTPs) also need to have the
flexibility of being able to control other NDS users' sites. This would enable overlapping
access and the resultant ability for these units to contact their resources throughout their
AOR's, without intervention by operators from the other units.
B. NDS PUBLIC COMMUNICATIONS REQUIREMENTS
Because the NDS also functions as a communications interface with the public,
there are certain present and future requirements placed upon the NDS from a CG-public
aspect.
1. Established Requirements
a. Digital Selective Calling
The United States, as signatories to the International Maritime
Organization (IMO) conventions, has agreed to participate in the Future Global Maritime
Distress and Safety System (FGMDSS). The FGMDSS
.. Will provide comprehensive distress and safety communications and require
establishment of new procedures. The system will take advantage of recent
technological advances to significantly improve the safety of life at sea. [Ref. 19:p.
I-1]
The FGMDSS is a complete system which will provide seven functions
through use of MF, HF, VHF and satellite communications technology. Those seven
functions are:
49
e alerting
e SAR coordination communications
e on-scene communications
e mcteorological, navigational, and urgent information
e locating
e general business communications
e VHF-FM bridge-to-bridge communications
The FGMDSS includes in its communications and alerting capabilities
Digital Selective Calling (DSC) and Narrowband Direct Printing (NBDP). DSC is an
alerting and circuit establishment feature very similar in function to the public switched
telephone network's signaling system. It enables the automatic initialization of
communications from one transceiver to another. The DSC message contains an address
field that rings another receiver (either a specific receiver or all ships within radio range
of the transmitter); an identification field for the unit initiating the call; a field indicating
the nature of the distress, if any; a field for the location of the initiating unit; and a field
for the frequency to use for further communications.
Narrow Band Direct Printing (NBDP) is a single-channel, automated
telegraph system using transmissions at 50 baud. The transmissions are either duplex
using the Automatic Repeat Request (ARQ) mode or simplex broadcast using the Forward
Error Correction (FEC) mode. The Coast Guard is currently operating two NBDP
systems. NAVTEX is a broadcast system in the MF band transmitting navigational
50
warning information to ships at sea using NBDP. Simplex Teletype Over Radio (STTOR)
is used in the HF band for two-way communications in the duplex (ARQ) mode between
Coast Guard COMMSTAs and ships at sca, and in the simplex (FEC) mode to broadcast
NAVAREA notices, hydrographic reports, and high seas weather broadcasts.
The system capabilities and vessel carriage requirements are delincated
based upon the arcas in which the vessels will be operating. The region which involves
VHF communications is Area 1, which is defined to be within the coverage of
shore-based VHF stations [Ref 19:p. II-17]. The requirements placed upon the Coast
Guard's VHF-FM portion of its Telecommunications System include VHF- FM Digital
Sclective Calling (DSC) on Channel 70. The following requirements are anticipated:
The VHF remote stations under Group control will need to operate a dedicated DSC
watch on 56.525 MHz (Channel 70)... The current VHF base stations are
overloaded during peak periods. New basc stations will be required to support the
proposed FGMDSS frequencies if the current command and control (C2) system
operates in parallel with the FGMDSS. [Ref. 19:p. HI-11]
Implementation of these capabilities is scheduled for the mid-1990's, any
replacement of the NDS will have to take these treaty obligations into account and add
DSC capability to the NDS.
b. Broadcast NTM
As per the Coast Guard Telecommunications Manual, the Coast Guard
is required to transmit voice safety and information broadcasts on VHF- FM at specified
intervals. These broadcasts are usually carried out by Group COMMCEN radiomen
əl
simultaneously on the NDS sites and the Group's local MF transmitter (using 2670 kHz
USB). Scheduled broadcasts can last as long as 10 minutes and must be repeated twice
a day (every 12 hours) with unscheduled broadcasts made frequently during the day. This
requires a considerable amount of air time for both the personnel and the equipment,
preventing their use for other communications.
Another issue regarding safety broadcasts is that of communicating with
foreign vessels. The Coast Guard transmits safety broadcasts over Channel 22A. The
"A" after the channel indicates that it is used for duplex operation, according to the ITU.
The Coast Guard only uses one of the duplex channels within the U.S., causing any radios
configured for international use to be unable to receive the safety broadcasts sent out by
the Coast Guard. This inability has resulted in several near-misses and calls for some
sort of legislation to solve the problem (Ref. 20]. This inconsistency with international
practices and frequency assignments causes problems for foreign vessels transiting U.S.
waters. Any resulting legislation or regulations would place additional requirements on
the NDS. The general incompatibility issue is discussed further below in the section
regarding all-channel selectability.
c. Distress Communications
Most of the communications between the public and the Coast Guard
involves some sort of distress communications, either between the Coast Guard and a
distressed vessel or between the Coast Guard and a third vessel acting as a communi-
cations relay for a nearby distressed vessel. Because the NDS public interface is
primarily a distress communications system, it is essential that the NDS have the
capability to communicate with distressed vessels anywhere within the design parameters
(Appendix A). This is equivalent to the intra-CG requirement that Groups bc able to
communicate with their units anywhere within their AORs, just on different frequencies.
The primary CG distress communications requirement is that of guarding
Channel 16. This requirement is currently being fulfilled by the NDS through use of the
separate guard receivers at each NDS site, with one particular operational exception.
Group COMMCENS have the ability to guard Channel 16 no matter to what channel the
controllable transceivers are tuned, however they cannot hear traffic on Channel 16 when
they are transmitting on the NDS. For technical reasons, when the controllable NDS
transmitters are keyed, the Channel 16 receivers are muted. This prevents the reception
of distress traffic during the periods when the NDS is being used for Broadcasts or other
transmissions, and creates the probability of a distress call being missed during a
broadcast.
d. All-Channel Selectability
As indicated in Chapter III, the current NDS remote transceivers permit
a choice of only six channels. These channels are crystal-controlled, and can only be
modified through replacement of crystals at the NDS remote transceiver sites.
The institution of Channel 9 as a supplemental hailing channel [Ref. 21],
and frequent need to contact vessels on channels they normally monitor has made the six-
channel limit unbearable. The six-channel maximum forces most NDS transceivers to
select only six channels from the channels listed in Appendix E. NDS transceiver
locations that serve two Groups would have to include both group working channels in
53
the available six channels in order to provide service on both Groups' working
frequencies.
The channel limitations of the present system act to heighten the
overcrowded state of Channel 16. Distressed vessels that are willing or able to shift to
other frequencies frequently do not have the frequencies available at the NDS sites for
use, and the NDS equipment does not have the frequencies available that the distressed
vessels can use. As indicated above, there are also problems regarding communications
with foreign vessels carrying radios configured according to the ITU international
VHF-FM guidelines. The need for access to all channels is evident.
e. VHF-FM Radio Direction Finding
Past incidents of distressed transmission location detection and present
incidents of distress/hoax transmissions have initiated a need for a VHF-FM Radio
Direction Finding (RDF) ability, at least on VHF-FM Channel 16 [Ref. 22:p. 1]. As
previously mentioned, many CG stations have localized RDF capabilities for obtaining
a RDF bearing on the marine band or EPIRB/ELT frequency, but the NDS currently has
no RDF network. The creation of a RDF network for the NDS has now become a
priority for the Coast Guard [Ref. 22:p. 1].
The cost benefit of coastal RDF networks was investigated in a study
performed in 1986 [Ref. 23]. The study examined the cost of installing RDF equipment
versus the savings in operating expenses resulting from reduced search operations because
the location of the distressed vessels was provided by the RDF network. The general
results indicated that:
54
... the installation of VHF-DF in some Coast Guard Groups is a very favorable
proposition. In a least nine of the groups studied, a VHF-DF system will pay for
itself in reduced Operating costs in less than five years. An investment in VHF-DF
made now will save money well into the foresceable future. (Ref. 23:p. 28]
It should be noted that no analysis was made of possible additional lives
or property saved as a result of the use of the RDF net, only the reduced operational
costs. Any benefits in additional lives or property saved would be over and above the
savings indicated in the study. The conclusions of the study echo this concept:
One should also consider the potential for saving additional lives and property
through use of VHF-DF. Although it was not possible to predict the savings in
lives and property, it is possible to look at the historical potential. For those areas
(cells) that have a payback period of less than five years, based on the benefit-cost
analysis in Appendix D, there were 42 lives and $7.4 million worth of property lost
during FY83 and 84. The savings of only one life or even of only ten percent of
the property lost would compensate for the $250,000 to $350,000 cost of VHF-DF
equipment for the cell during the first year of operation. [Ref. 23:p. 28]
As mentioned above, there is not at this time any capability for
performing VHF RDF using the NDS sites. Considerable intercst, however, has arisen
in having RDF capabilities added to the NDS. A pilot project between MLC Pacific and
Commander, Fourteenth Coast Guard District will be installing remote RDF bearing
equipment at the four NDS sites in Hawaii in the near future. The recent incident with
the F/V Sol E Mar off of Cape Cod accentuates the need for some sort of RDF network
along the coasts for SAR and hoaxes, and has sparked Congressional interest and funding
towards the establishment of a VHF-FM RDF network [Ref. 22]. And a project has been
55
proposed to evaluate the various RDF technologies at the Coast Guard Academy İRef.
24].
2. Potential
a. Differential Global Positioning System Transmissions
The Global Positioning System (GPS) satellite navigation netvvork permits
accurate terrestrial positioning to within 100 yards for civilian vessels at sea. A value
added service of GPS, called Differential GPS (DGPS), permits transmission of a
localized correction factor from terrestrial transmitters which increases navigational
accuracy to within tens of yards for maneuvering in pilotage waters. Due to limitations
on thc GPS satellites, this dGPS signal has to be transmitted to the GPS receiver
separately from the GPS signal itself. The GPS satellites also lack the ability to blink,
or notify their users when one of the satellites is transmitting incorrect signals, thereby
making the navigational information from that satellite suspect. In addition to providing
higher accuracy signals, the dGPS signal could also be used to carry out the GPS blink
function. Both the correction and blink signals are provided by a GPS monitoring center,
which monitors the status of the GPS network.
At this time there have been experiments using CG-operated MF
radiobeacons to transmit the dGPS signal. Because of the lack of connectivity of the
radiobeacons--most are placed in remote areas with only power connections--they are
ill suited to be connected to the GPS control center for use in transmitting the dGPS
signal. The NDS sites and VHF-FM transmitters may be called upon to provide better
56
connectivity and coverage for the dGPS signals. This would be especially true if the
NDS were, for other reasons noted above, provided with true network connectivity.
b. VTS/MARDEZ interface (secure)
As part of the Maritime Defense Zone (MDZ) Harbor Control system, the
CG Vessel Traffic Systems (VTS) need the ability to communicate with MARDEZ
resources over secure VHF frequencies. At present, most VTSs have their own remoted
transceivers for use from their OPCENS while communicating with the vessels transiting
the waterways under their control. These transceivers (Appendix C) do not currently have
the ability to communicate via secure means. If the NDS is provided the capability to
transmit and reccive using secure means, access to the system by the VTSs would prevent
their having to also buy secure-capable transceivers of their own.
c. Dependent Surveillance
There has been considerable interest in the Coast Guard regarding
dependent surveillance of vessels [Ref. 25]. Dependent surveillance can be defined as the
ability to determine the position of a vessel through transmissions from the vessel. This
definition would eliminate radar, but would permit location via transmissions from the
vessel itself, either providing the location from onboard navigational equipment or
enabling shoreside RDF to locate the vessel.
An experiment in the early 1980's tested the possibility of dependent
surveillance of CG vessels. The so-called "Hampton Roads Testbed," named for the
group where the project was installed, plotted location information from CG vessels on
57
a Graphical Analysis, Archiving and Display Station (GAADS). This information could
then provide vessel track history, near-real-time positioning of resources, updated buoy
locations and status, and calculation of intercept information for the vessels. Results from
the experiment indicated that this dependent surveillance was beneficial to the group users
[Ref. 26:p. 31].
It should be noted that Digital Selective Calling has the inherent ability
to transmit positional information within its polling and ship's position calling sequences.
The DSC transmitter aboard the vessel can be configured to transmit the ship's
position-- provided by onboard navigation systems such as dGPS or LORAN--at regular
intervals or when polled. This would in effect broadcast the location of the vessel to all
DSC receivers, including the NDS DSC-equipped receivers. Adoption of the DSC
standard for dependent surveillance would require similarly-equipped DSC transceivers
at NDS sites, but would provide near real-time positioning information for VTS
dependent surveillance use.
58
V. EVALUATION OF SELECTED TECHNOLOGY
Due to the specific nature of VHF-FM communications, there has been only a
limited amount of research regarding the topics of VHF-FM RDF, DSC and VHF packet
switched networks. In this chapter, the author evaluates the available VHF-FM tech-
nology and surveys the applicable research that has been conducted.
A. RADIO DIRECTION FINDING
The primary user of large radio direction finding systems in the United States is the
federal government. Various agencies maintain direction-finding equipment and networks
for lavv enforcement and national defense. In the military, radio direction finding (RDF)
falls under the general topic of electronic warfare (EW) or electronic intelligence
(ELECINT). As such, it is used by ships, aircraft and land units as a passive method of
locating a radio transmitter.
In the civilian world, RDF units are used by boaters and aircraft for navigational
purposes. These vehicles utilize the various networks of radiobeacons established for
navigation and position determination.
Because VHF is a relatively short-range line-of-site communications medium,
there has been little research involving VHF DF. Considerable effort has been expended
in HF DF research and HF DF networks; however, due to the differences in propagation,
this research is not applicable to WHF. The author was able to locate one WHF study
performed in 1978 by the Department of Transportation's Transportation Systems Center
59
in Cambridge Massachusetts for the Coast Guard involving Coast Guard units [Ref. 27].
This study evaluated RDF techniques for shore-based position locating using discrete DF
equipment. The study surveyed available DF techniques, developed an analytical model,
performed error analysis of the equipment, and conducted a field test of the systems. The
conclusions of the study were that:
shore-based DF was shown to be a valuable SAR tool
shore-based DF was valuable for locating EPIRBs
DF performance is critically based upon antenna placement
synthetic doppler antennas are better than Adcock arrays
graphical display of bearings was preferred over digital
it was desirable to remote the DF antenna via phonc lines
(Ref. 27:Chap 5:p. 1-4]
The recommendations of the study were that:
the CG proceed with a thorough DF test and evaluation
the DF antenna be the same height as the comms antenna
the DF antenna site minimize local signal reflections
a systematic site evaluation procedure be developed
commercial units should be modified to increase sensitivity
60
e the IDFM DF system should be further evaluated
[Ref. 27:Chap. 5:p. 3-4]
It should be noted that the last recommendation refers to a direction finding
technique, induced doppler FM (IDFM) that can determine both the bearing to the
transmitter and the range. At the time of the study there was no equipment that used the
IDFM technique, but the testers believed that the technique showed promise. Unfor-
tunately, none of the systems surveyed by this author use the IDFM technique.
1. Discrete Systems
As previously discussed, discrete systems are those that directly or remotely
determine the bearing from the RDF antenna to the transmitter and display it to an
operator. These systems are usually small, inexpensive, and reasonably accurate.
There are numerous manufacturers of discrete RDF systems, for a listing see
Appendix D. Most of the commercial marine units are designed for use by boaters to
provide lines of position from the Coast Guard's network of MF radiobeacons located at
or near major nautical reference points (e.g., inlets, headlands, etc.). They are also able
to receive commercial broadcast frequencies and use those transmissions for localizing
their positions.
In addition to the marine units, there are numerous specialty units produced
for use by military vehicles, vessels and aircraft. These units provide the ability for
determining relative bearing of a transmission source and enable the unit to "home in" on
61
the source. These are used for locating navigational beacons, emergency beacons
(EPIRB/ELT) and for tactical use in locating enemy transmitter sites.
Discrete systems are compact and inexpensive, and are useful when a single
line of position or bearing is desired. They are installed aboard most CG vessels and
aircraft and are used for both navigation and homing in on a signal. In limited cases the
bearings from multiple sites are combined manually to provide a triangulated position.
It is very uncommon, though, to find a discrete system that provides any type of record
of the bearings. In other words, discrete systems are definitely "real time" systems, with
no method of recreating the information once the signal has ceased, unless a written
record of the bearing is maintained by an operator.
In most instances, these discrete systems are unable to share information
between multiple sites automatically. Any triangulation of a transmission received at
more than one RDF site must be performed manually by an operator, and plotted
manually on a chart of the area. It is for this reason that integrated systems have been
developed to automate this process and analyze the information provided by multiple RDF
receivers.
2. Integrated Systems
As indicated previously, integrated systems use bearing information from
multiple receiver sites and computer technology to process the data and provide locations,
not just bearing lines or lines of position (LOP). A typical result using new technology
is a geographical display of the area showing lines of position from the RDF sites inter-
secting at a point surrounded by a probability ellipse to indicate the detected location of
62
the transmitter (Figure 8). Additional display information includes bearings from each
RDF antenna and a bearing/range from a shoref location, in this case Coast Guard Station
Shinnecock. Enhancements to these systems permit the display of relative signal
strengths, the manual inclusion of bearing data provided by RDF units not connected to
the system (c.g., from a nearby vessel), and even spectral analysis of the signals in order
to differentiate between two simultaneous transmissions on the same frequency.
The Canadian Coast Guard has had an integrated system installed in Georgian
Bay, Canada for several years. This system has the capability for eight remote RDF sites
but is currently in operation using only two remote sites. This system has the advantage
of including a color printer which can provide a hard-copy output of the screen display,
thereby solving the problem of recreating or storing the signal and bearing information.
In the U.S., the Federal Communications Commission (FCC) currently
produces and operates their own integrated RDF equipment which functions over a very
broad frequency range, 30 MHz to 1 GHz. The Coast Guard has made use of the FCC's
installed system of four remote sites in a major coastal metropolitan area for RDF of
distressed vessels, hoaxes and false alarms. The Coast Guard has also provided funding
for the FCC to install a joint-use system of eight remote sites in a second coastal
metropolitan area. Besides the FCC, there are several manufacturers of integrated RDF
systems; these are listed in Appendix D.
The FCC system has many positive features as an integrated RDF system.
The operator interface is very "user friendly." The control software permits the Central
computer to remotely control the frequency of the RDF receiver at the antenna site.
63
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64
Frequencies can be selected as channels instead of frequencies if desired, permitting the
operator to select "channel 16" instead of trying to remember and then input 156.8 MHz.
The use of dial-up modems enables the remote sites to be called and controlled by
Operators at an alternate central computer site. The efficient user interface also permits
weak or spurious signals to be disregarded, or additional RDF LOPs from other sources
to be added into the plot and subsequent calculations. Easy as the interface is, however,
the operation of the network is at such a level that it would take considerable training for
a user to become proficient and effective.
An issue that the FCC has successfully dealt with is the placement of the RDF
antennas. If the antennas are placed near other radiating sources, they suffer from those
strong signals, and are unable to effectively DF weaker signals. The FCC places their
antennas in relatively quiet RF areas in order to minimize interference from other sources
of electromagnetic interference.
Unfortunately, the FCC systems lack an essential feature that is necessary for
the Coast Guard's use of RDF as an effective distress location tool. For economy, the
FCC systems use dial-up access vice leased lines to the remote receiver sites. This
requires that the operator initiate a call between the central computer and the remote sites
to establish a circuit before bearings can be obtained from the RDF equipment. In the
event of only one short distress call being transmitted by a vessel, as was the situation
in the recent case of the F/V SOL E MAR [Ref. 28] off of Cape Cod, this system would
take too long to activate. Even a feature such as an instant recall, a "go back 15 seconds"
button such as installed in the RDF systems in Miami and St. Petersburg, would be too
65
limited for truly efficient use. It is clear that some sort of permanent signal and bearing
storage method needs to be included in any RDF system.
Chapter III discussed the integrated RDF systems that the Coast Guard has
installed and operational. These systems have proven to be of only limited use due to
reliability and sensitivity problems. Also, if the multiple antenna sites are in a relatively
straight line, there are limited locations where a three-line fix can be obtained due to the
strength and line-of-site nature of the signal.
Besides the Coast Guard and the FCC, another user of integrated RDF
equipment is the Federal Aviation Agency (FAA). The FAA has VHF-FM RDF sites at
all Automated Flight Service Stations (AFSS) and major Flight Service Stations (FSS)
throughout the U.S. These units are able to control up to 24 separate stations and
provide triangulation and graphics plotting capabilities to the FCC control station. The
remote sites can be controlled from as many as four central units, thereby enabling more
than one master unit to access remote sites. In addition, the system has the ability to
track and display the locations of up to ten aircraft simultaneously, and to display data
about individual airports, obstructions, or navigational aids. The FAA system also has
an "emergency mode” with the ability to automatically show course and distance
information from a distressed aircraft to the six nearest airports. [Ref. 29]
The FAA's system has the same benefits as the FCC's, with the addition of
being able to display geographical data regarding navigational aids, facilities, etc. The
FAA's system is also commercially made, and would not be restricted in its deployment
by the limited production capacity of the FCC.
66
The FAA s system suffers from the same dial-up modem requirement that
affects the FCC system. But the manufacturers of the FAA's equipment claim that their
bearing data can be provided in less than One second. However, this does not solve the
bearing storage and recall problems noted above. Finally, the FAA's system is optimized
for the frequencies between 118 MHz and 136.975 MHz; they would have to be modified
for CG use.
B. VHF-FM TRANSCEIVERS
The standard VHF~FM marine~band transceiver has matured into a very compact
and feature-laden communications device as a result of advances in electronics
technology and fabrication. Most units are fully synthesized, able to operate over all 54
transmit channels and 85 receive channels (including the National Weather Service
weather channels) and available in either hand-held or installed configurations costing
less than $500. Output is switchable and ranges from one watt to a legal maximum of
25 watts. Compact size and weatherproofing enable even an open boat to have a
user-installed VHF-FM marine radio aboard.
Gone are the days when SSB or DSB AM radios had to be installed and tuned by
the technician, who required large grounding plates and cumbersome antennas to make
the equipment work. The VHF-FM transceivers provide clear interference-free
communications between boats within line-of-site distances and with the Coast Guard's
NDS out to 30 or 40 miles, as a general rule. Distressed calls are more efficiently
67
made--the Coast Guard no longer has regular beach patrols or manned watchtowers in
most areas scanning the seas for distressed flares or evidence of a wreck at sea.
The author was unable to locate any applicable research regarding VHF-FM
transceivers or transmission. Like VHF-DF, this topic is so specialized that it is unlikely
there is much research available. VHF-FM modulation techniques and transmission
equipment has progressed to such an extent that it is a mature technology.
Despite the advances in VHF-FM radios, most of the newer features contained in
these general purpose transceivers are still not available for use within the Coast Guard.
As noted above, the Coast Guard needs to maintain a Channel 16 guard, to transmit and
receive encrypted voice, and to have remote control of the NDS transceivers. As a result,
the radio equipment purchased by the Coast Guard is usually supplied by one of the
major vendors of commercial telecommunications equipment. These manufacturers are
usually not as quick to provide the newer features, preferring to provide upgrades to the
present equipment. This limits the capabilities of the systems provided, especially in the
areas of channel selection, encryption, and Digital Selective Calling (DSC).
1. Channel Selectivity
Current technology from Motorola, the manufacturer of the installed NDS
equipment, limits the number of remotely-controlled channels to 12. This limitation is
caused by the availability of only 15 in-band signalling function tones. Twelve tones are
used for switching among the 12 channels and the remaining three are used for other
transceiver functions. The presence of this in-band signalling also precludes the use of
standard 1200 baud or higher modems over these radios due to conflicts between the
68
modem tones and function tones, as identified in the Low-Cost Packet/SITOR
experiments [Ref. 17]. A shift to another manufacturer that provides out-of-band
signalling would be costly, due to encryption incompatibilities discussed below.
2. Encryption
The Coast Guard presently has an installed base of DES-encrypted VHF-FM
transceivers--the MCX 1000 mobile radio with channel 16 guard and the MCX 300R
handheld radio. Both of these use the standard DES encryption algorithm for secure
communications at the encrypted for transmission only (EFTO) level in the marine
VHF-FM band.
The DES encryption provides secure but not classified communications over
the radio. Other federal agencies such as the U.S. Customs Service (USCS) and the Drug
Enforcement Agency (DEA) use DES radios for communications. Because the present
radios are capable of operating in the government band from 162 MHz to 174 MHz, the
Coast Guard has compatibility with these other agencies and can therefore establish secure
radio communications with them. The radios are relatively easy to code and operate, and
have proven to be very useful. They are not without their problems, however.
The implementation of the standard DES encryption algorithm by Motorola
produces transmissions which are not compatible with DES radios manufactured by other
companies. As a result, the Coast Guard would have to replace not only its NDS
transceivers, but all its DES-encrypted radios 1f it were to change transceiver manufac-
turers for its encrypted transceivers. Because of this, the Coast Guard is limited to the
technology that Motorola can provide, unless another company builds equipment that
69
follows Motorola's DES bytestream pattern. A second problem with the DES transmis-
sion is a loss of signal strength by approximately 3dB resulting from the conversion of
the analog voice signal into a digital signal at 12kbps. This limits the range of the
handheld MCX 300R units to nominally only three or four miles.
3. Digital Selective Calling (DSC)
The DSC implementation is still in its infancy here in the United States, but
has already been installed and tested along the Danish coast (Ref. 30]. The use of DSC
will be mandatory for vessels greater than 300 tons and vessels carrying six or more
passengers constructed after 1 July 1995. All similar existing vessels will be required to
have DSC-compatible radios by 1999 (Ref. 31].
Little research was found regarding VHF-FM DSC technology. The CCIR
standards are still in the draft stage and the technology is still being developed. The only
study located proposed a mathematical model to determine if one DSC channel would
suffice to provide an acceptable grade of service for both commercial calling and distress
calling. The results of the study indicated that one channel was sufficient, based upon
there being 19 single-frequency channels available for commercial calling (Ref. 32:p.
106]. The total number of available channels may change, however, due to the planned
reduction in the VHF-FM marine channel bandwidth from 25 kHz to 12.5 kHz. This
bandwidth reduction would double the number of available channels and therefore place
approximately double the load upon the DSC channel. One channel may therefore no
longer be enough for both distress and commercial calling.
70
The currently-available DSC-equipped units in the U.S. have the standard
DSC features plus some additional features that would be of great value to the mariner.
Because DSC permits what are in essence station-to-station circuit-switched calls, there
is need for some sort of directory service. The current implementation permits this with
a large (99-200 number) scrollable directory for calling other DSC radios. This scrollable
directory enables the caller to scroll through the directory until the radio call sign (or
alternately the registration number or vessel name) of the callee is found, and then to
initiate a call to the callee with a keystroke. If the callee's radio is active, the callee 1s
alerted and can respond to the call. If the callee does not answer, the caller's call sign
is stored in a 100-number "call waiting" directory within the receiving unit. An
additional 99-200 number directory is provided in which to store shoreside telephone
numbers. Ultimately DSC-equipped vessels will be able to make automatic connection
requests via DSC-equipped marine operators into the public switched telephone network,
creating a mobile-to-shoreside phone capability similar to cellular telephones. All of this
is made possible using the DSC channel 70 as a control circuit to establish radio commu-
nication circuits between two DSC transceivers.
An automatic alerting feature is also installed in the DSC transceiver.
Activation of this feature transmits an emergency message packet to all radios within
range, causing them to produce an audible signal and display the sender's identification
(1.e., callsign, vessel name, or vessel registration number). If the distressed vessel has a
navigational device (e.g., LORAN or GPS receiver) connected to the DSC radio, the
vessel's position can be transmitted in the packet. This enables the distressed vessel to
TI
transmit the vessel's identification, location, and nature of distress automatically. A
similar feature enables DSC transmitters to make "all ships" calls for broadcasting safety
or weather information.
The Coast Guard is Investigating the installation of a DSC transceiver as a
remote for the NDS site in St. Petersburg, Florida. Implementation would require one
receiver and two transceivers; one receiver for Channel 16 guard, one transceiver for
Channel 70 (DSC channel) guard and a transceiver for general communications. Control
of the equipment would be via the standard Motorola NDS remote control unit. Receipt
and processing of the DSC information from the Channel 70 transceiver would be
managed by an application running on a Coast Guard standard microcomputer. Atthis
point, there are very few manufacturers of DSC equipment in the United States. The
Federal regulations have not yet been adopted, and final standards have not been
established. Unless its use is also mandated for recreational vessels, the DSC implemen-
tation will be only a partial solution. It could even prove to be a safety hazard for
recreational vessels. Once they are DSC-equipped, commercial vessels will no longer
monitor Channel 16, and there would be no way for recreational vessels to contact the
commercial vessels for assistance or for preventing collisions without using DSC.
C. RADIO PACKET SWITCHED NETWORKS
In packet switched networks, data is sent using packet switching technology, where
the information is broken down into small quantities, encapsulated in packets and
transmitted. These packets contain both administrative information (address, routing, etc.)
and the message itself. Receivers acknowledge for and keep only the packets addressed
to them, discarding any packets addressed to other stations. Packet switching is used for
connectivity between computers in terrestrial local area networks (LAN) such as Ethernet
(IEEE 802.3) or IBM's Token Ring networks (IEEE 802.5). These LANs use a solid
medium for the transmission of the packets, usually either copper or fiber optic cable.
Radio packet switched networks (RPSN) use radio waves as the transmission to
create wide area networks (WAN). The presence of radio packet switched networks is
hampered by limited available frequencies and transmission bandwidth. At present, there
are only a few RPSNS in existence, and only limited equipment for use with RPSNs. The
military uses special packet-switched radio systems for battlefield communications, but
these are not really suitable for the Coast Guard's needs.
Considerable research has been performed regarding radio packet switched
networks. As far back as 1974, the Defense Advanced Research Projects Agency
(DARPA) funded studies regarding radio packet switched networks. Topics investigated
included network capacity, configuration, topology, routing and transmission range [Ref.
33, 34]. Further research continued to investigate these topics as well as the use of
satellite links in terrestrial RPSNs and the use of broadcast networks [Ref. 35, 36].
1. ALOHA Network
The first large-scale radio packet switched network was the ALOHA system
developed at the University of Hawaii in 1971. This was a packet switched system using
duplex VHF-FM frequencies to connect the seven campuses On four islands to the
mainframe computer on the island of Oahu. Transmissions from different remote stations
73
to the receiver at the mainframe were subject to contention and collision, but trans-
missions from the mainframe to the remote sites were not subject to either contention or
collision. Packets sent from the remote stations and successfully received by the
mainframe were acknowledged by the mainframe. If a packet was not acknowledged in
a certain amount of time, the remote station assumed that the packet was lost due to
collision and, after a random time-out period, retransmitted the packet. Stations were
frec to transmit packets on demand; there was no monitoring of the frequency to
determine if it was already in use by other stations. This transmission method is now
termed Pure ALOHA. [Ref. 37:p. 182-185]
The ALOHA network was a success. It permitted efficient two-way data
communications without the need for expensive and unreliable telephone lines.
The ALOHA protocol had its drawbacks, however. The best that can be
hoped for is a channel utilization of 18%, which is much less than most users would find
acceptable [Ref. 37:p. 123].
A variation on pure ALOHA is slotted ALOHA, which prevents stations from
transmitting until a time signal is given. This essentially doubles the throughput of the
ALOHA system to 36%. For a full explanation of the efficiency of ALOHA and slotted
ALOHA sce Ref. 37:p. 121-124.
2. Graphical Analysis, Archiving and Display Station
The Coast Guard first experimented with a radio packet switched network in
1982. This system was called the Graphical Analysis, Archiving and Display System
(GAADS) [Ref. 26], and was actually an integrated system of vessel location, com-
74
munications and geographical data display. GAADS was better known as the "Hampton
Roads Testbed," named after its test site, Group Hampton Roads (GHR) Virginia.
Initially GAADS began as a project to communicate with and track underway CG vessels
and to maintain a shore-side data base for storage, processing and report generation.
These three systems were called the Mobile Digital Communications Subsystem (MDCS),
the LORAN C Navigator (LONA) and the Shore Based Network (SBN), respectively.
The system was based upon one used by the City of Miami Police Department to track
and communicate with its patrol cars. GAADS used a polling scheme, communicating
with each vessel at ten-second intervals to pass location information and messages back
and forth via the MDCS between underway units and the SBN.
A further enhancement to the system resulted in the creation of the GAADS
terminal, which enabled the shoreside operators to see the vessels' locations plotted on an
electronic chart of the area. Other features of GAADS included:
e bcaring and range calculations
e an electronic maneuvering board
e track histories of single and multiple vessels
e ability to change charts electronically
e ability to zoom in on charts
@ vessel intercept calculations
e ability to generate search patterns
73
e ability to plot voyage waypoints and display buoys
e ability to store/recall data on a floppy disk
GAADS suffered from equipment reliability and vessel availability problems.
Acceptance of the system by users was mixed. Communications with the vessels was
considered secondary to the basic locating and plotting features. Results of the study
included:
e GAADS successfully provided GHR with near real-time
e graphic displays of resource and target locations
e resource position monitoring during SAR cases was found
to be important
e automatic generation of search patterns was found to be a
useful capability
e the ability to zoom-in the electronic charts was valuable
e the ability to display track history was useful
e the capability to automatically plot and monitor search
pattern execution saved time and effort [Ref. 26:p. 31-34]
One project that has evolved from the GAADS research is the Geographical
Display Operational Computer (GDOCS). GDOCS is scheduled to have features similar
to those tested in the GAADS project, with the ability to provide facility information, plot
76
search patterns, track vessel locations, permit CG database queries, and plot RDF
bearings. The present GDOC proposal does not include any data communications
facilities, however. Plans are for GDOC to be placed at Groups, AIRSTAs and
MSO/COTP OPCENS. [Ref. 18]
3. High Frequency Data Link (HFDL)
The High Frequency Data Link (HFDL) currently in use by Coast Guard units
is a radio packet switched polling WAN, which provides data link connectivity between
cutters and Coast Guard COMMSTA's designated as net master stations. Transmission
is in the HF band and encryption is possible to the SECRET level using the KG84C
encryption device. A diagram of the HFDL is shown in Figure 8.
The polling occurs when each secondary station is queried, in turn, by the
master station. The master station sends a query packet addressed to each specific
secondary station asking for a response. Secondary stations that have no traffic respond
to the poll with a "no traffic" report. Secondary stations having traffic transmit their
traffic when polled.
Polling of stations by a master station guarantees that the presence or absence
of a station is noted by the master. Lack of a response to a poll by a secondary unit
alerts the operators at the master station to the fact that contact has been lost with that
particular secondary station. Polling also ensures that each station is given an Opportunity
to send its traffic without contention between stations. Polling is a form of time division
multiple access (TDMA) where each secondary station is given a slice of time to send its
traffic; the signal marking the time slice being the poll from the master.
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78
Polling, however, clutters the spectrum with polling transmissions and
responses even if there is no traffic to pass and prevents the passing of traffic until a
station is polled by the master. Polling also requires that the master station know the
address of cach of its secondary stations. Polling prevents the secondary station from
transmitting traffic or alerting the master station at times other than when that secondary
station is being polled. Unless used for a limited number of stations, polling would not
permit a rapid two-way communications link, such as would be needed by an underway
unit querying a shoreside database.
An alternative to polling is the use of a carrier sense multiple access/collision
detection scheme (CSMA/CD). CSMA/CD permits traffic to be passed to the primary
stations by the secondary stations on demand. Each secondary station transmits when it
has traffic to pass, and only when it senses that there are no other carriers using the
frequency. Note the difference here between CSMA/CD and ALOHA. ALOHA trans-
mitted whenever there was traffic, without first checking to see if there were packets
already being transmitted by another station. As can be imagined, even with CSMA/CD
there will be times when two or more secondary stations would hear no carrier and both
transmit simultancously, thereby causing collisions. The collision detect algorithms must
account for these collisions and provide for a method to detect them and to retransmit the
traffic. The AX.25 protocol used by amateur radio packet systems is considered
CSMA/CD, but is limited in its ability to "carrier sense" due to the line-of-sight nature
of VHF communications and the so-called "hidden transmitter" problem. In the "hidden
transmitter" problem, two transmitting stations may not be able to sense cach other's
79
carriers due to their geographical separation, but a third receiving station between the two
stations would be able to receive signals from both distant stations. If one of two distant
stations transmitted (the hidden transmitter), the second would not be able to sense the
first's carrier and would transmit, causing a collision. In this manner, the carrier sense
phase of the protocol would fail to function, but the collision detection and retransmission
would correct for the collision.
4. Amateur Radio Packet Switched Networks (AX.25)
The AX.25 protocol was developed by amateur radio for use in RPSNs and
is a variant of the CCITT X.25 level 2 packet protocol used by terrestrial wired packet
switched networks. The additional features in AX.25 include an extended address field
(to permit the inclusion of up to eight addresses for routing) and the addition of an
Unnumbered Information (UI) frame for use in transmitting beacons to multiple stations.
Amateur RPSNs consist of a computer terminal, a radio (either HF or VHF)
and a dedicated terminal node controller (TNC) which acts as the packet as-
sembler/disassembler (PAD) and contains the hardware for the AX.25 protocol. TNCS
are inexpensive and readily available from commercial sources, terminals can run any
basic data communications program, and standard VHF-FM radios can be used. Amateur
radio operators have created vast networks of VHF and HF packet radio bulletin boards
and simplex FM digital repeaters (called digipeaters) and are able to transmit message
traffic nationwide. The AX.25 protocol permits packets to be sent "in the blind," that is
without a specific address for the receiver. This enables beacon operation and broadcasts
of announcement messages without the need for polling.
80
Packet radio networks have a limit to their cfficiency, due to the possibility
of collision and packet retransmission. Heavily-loaded systems will slow down
considerably due to this need for packet retransmission. Multi-hop transmissions
especially suffer degradation in throughput from the "hidden transmitter" problem. The
Coast Guard has experimented with Radio Packet Switched Networks using amateur radio
technology [Ref. 17]. This experiment showed that secure two-way packet radio
communications could be successfully conducted using Motorola DES radios and off-the-
shelf TNCs. Data transmission rates of 1200 baud were casily attainable, except when
using NDS equipment. The problem was an incompatibility between the NDS hardware
and the modems. The standard Bell 202 modem tones used to transmit data interfere with
the Motorola function control tones and prohibit transmission over the current NDS
equipment at rates greater than 300 baud. Overall, however, the experiment proved the
feasibility of using AX.25 protocol and inexpensive off-the-shelf equipment to transmit
and receive data between Coast Guard units in a secure mode.
81
VI. SUMMARY AND RECOMMENDATIONS
As the preccding chapters havc shown, thc recapitalization of the National Distress
System brings with it a myriad of details. Its replacement must be orchestrated within
the Coast Guard and coordinated among other agencies in order to effectively deal with
the related initiatives currently underway.
It is evident from the applicable technology that the equipment and systems exist
or are being developed to fulfill the requirements put forth in this thesis. The more
mature technologies of VHF-FM transceivers and radio direction finders are being joined
by systems which provide DSC and radio packet communications. All of the needed
technologies exist as separate pieces, what is required now is for the Coast Guard to work
towards the integration of these various systems into one NDS network. The resultant
system would be able to fulfill the requirements and provide options for expansion well
into the next century.
A. FUNCTIONAL MODEL
A result of this research has been the development of one possible functional model
of the NDS that would fulfill the requirements discussed. This model provides a
graphical representation of the radio frequency information flows and the general
architecture of the system up to the Group level.
The radio frequency information flows are detailed graphically in Figure 9, along
with the equipment necessary to manage these flows. It should be noted that these flows
carry both internal Coast Guard C* traffic and communications between the Coast Guard
and the public. Any move to separate the internal Coast Guard C^ communications
network from the NDS will have to take this into account.
Figure 10 shows the recommended NDS remote site configuration. The equipment
indicated reflects what would be needed to transmit/receive and manage the information
flows shown in Figure 9, and is all readily available from commercial sources. There are
two specific items that are of note, that of the RDF antenna controller and the use of
Integrated Services Digital Network (ISDN) telephone technology.
The RDF antenna controller is needed to enable the Channel 16 Guard receiver to
connect to both the communications antenna and the RDF antenna. It is assumed that the
default configuration for the guard receiver would be for it to be connected to the RDF
directional antenna, ready for use with the RDF system. The RDF antenna controller also
permits the general communications transceiver to access the RDF antenna and perform
RDF on any of its marine or government channels. When the general-purpose
communications transceiver was using the RDF antenna, the Channel 16 guard receiver
would be connected to a regular antenna on the tower to maintain the Channel 16 guard.
The use of ISDN technology enables the two voice signals and the packet switched
information to flow over the same ISDN Basic Rate Interface (BRI) channel. The BRI
channel contains two B (64kbps) voice/packet and one D (16kbps) packet channels. The
two voice signals, the Channel 16 guard and the general communications transceiver,
would share one B channel by using Adaptive Differential Pulse Code Modulation
(ADPCM). ADPCM enables analog voice to be digitized and occupy only 32kbps; a
83
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85
multiplexer would permit both voice signals to use one ISDN B channel. The other B
channel would be able to carry all the packet switched information necessary, and would
still have a reserve capacity for additional data from sensors or other communications
devices. The D channel would not need to be used, unless mandated by one of the
systems for signalling or control.
Figure 11 shows what the configuration would be at the Group or COTP
OPCEN/COMMCEN. Note again that all the equipment is available now. The only
developmental items are already underway, that of integrating the data outputs from the
DSC radios and the RDF receivers into the GDOC displays on the Coast Guard Standard
Workstation.
Included in the connectivity of the NDS is a link to the X.25 network being
installed by the Coast Guard, the HDN. In order for the NDS to be a true com-
munications network, this connectivity is essential. All that would be needed to complete
the connection would be basic routing hardware and software. Addition of dynamic
routing of data from the HDN to the deployed unit via the NDS data channel would
enable cellular-like communications as a unit moved along the coast. The routing tables
would be updated every time the unit transmitted its location to the GDOC, which passed
the routing information to the District or Area COMMCEN router. The routing
information could ultimately be maintained in a centralized database, much as AT&T's
Signalling System Seven will use.
A truly seamless network could be established if the routing tables were expanded
to include HFDL or satellite communications. A unit within VHF-FM range would have
86
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67
its data traffic routed via the VHF-FM data channel. If it moved out of VHF-FM range,
its onboard communications manager would reroute the traffic via HFDL or satellite.
This would reduce unnecessary HFDL load and provide communications system redun-
dancy.
One question that arises regarding both the internal Coast Guard data channel and
the public broadcast data channel is what frequency to use. As can be seen in Appendix
E, all the VHF-FM marine channels are already assigned--there are no channels
currently available for use in transmitting data (except DSC channel 70). There are,
however, other possibilities. The Government uses frequencies above 162 MHz, in fact
every Coast Guard MCX 1000 radio has some of these programmed in for use both
between Coast Guard units and when communicating with other agencies. One of these
frequencies could be used for internal Coast Guard simplex digital data. For the public
broadcast data channel, possibly one of the weather channels could be assigned for this
purpose. This would be appropriate because a portion of the Coast Guard's broadcasts
would consist of weather. If a currently-available channel (i.e., a weather channel) were
used, it would eliminate the need for the boater to purchase a new radio. The boater
would only need to purchase the interface (e.g., terminal node controller) between the
VHF-FM transceiver and his data terminal.
88
B. SYSTEM CAPABILITIES
In general, there are certain System capabilities that are necessary to fulfill the
requirements put forth in Chapters III and IV. These are, for the most part, available with
existing or planned technologies. These capabilities include:
@ remote controlled transceiver all-channel selectivity
@ DSC-capable transceivers
e integrated RDF systems with direction—finding data storage and retrieval
@ CG data channel transceivers
@ DES-capable transceivers
@ Public broadcast data channel transmitters
C. SYSTEM IMPLEMENTATION
1. Phasel - System Analysis
a. Project Manager
Prior to any further work being performed towards the VHF-FM NDS
recapitalization, it is imperative that a senior-level Project Manager be assigned. This
research indicates that there are many independent, ongoing initiatives that affect the NDS
recapitalization. These initiatives are being carried out by multiple commands scattered
throughout the U.S. The Project Manager is needed to coordinate these initiatives,
facilitate sharing of information and ideas among the different project officers, and direct
the thrust of the activities towards the goal of improving the NDS. Considerations should
89
be made to assigning an NDS Project Manager who would have both subject matter
expertise on the system, procurement experience, and proyected assignment longevity in
order to provide continuity over the length of the project implementation.
b. System Baseline
The next step in the implementation of the new NDS system would have
to be the creation of a system baseline, a "snapshot" of where the present system is. The
author found in his research for Appendices B and C that the data on the present sites
suffers from numerous discrepancies. These discrepancies cause differences in the site
data maintained by the various entities involved, the Districts, the Groups, the MLCS,
Headquarters, and the NTIA. One organization should be identified as the manager of
the official NDS database and act as the control point for NDS information, logically
within the Project Manager's office. Any and all changes to the baseline information
should be passed to this Database Manager. This would require that the maintenance
contracts for the NDS sites include a provision that all changes are reported to the NDS
database manager.
Not only is the site data different, but each site installation is different.
Reports from those involved indicate that documentation is lacking, circuits and cabling
are mislabeled, bonding of equipment is substandard, and security of the sites 1s, in some
locations, minimal. Prior to asking any contractor to bid on installing the new equipment
at the sites, it will be essential to bring all the sites to a minimal configuration and
documentation standard.
90
As previously noted, the creation of baseline information and standard
configuration is currently underway cast of the Rockies under the guidance of Com-
mander, Maintenance and Logistics Command, Atlantic. This baseline project needs to
bc expanded to cover all the NDS sites, including the limited NDS sites in Hawaii and
Alaska.
c. Standards Determination
Prior to drafting of the system specifications, it will be necessary to
establish or adopt standards for encryption, radio packet formatting, RDF data
transmission, and others. In many instances the standards have already been specified,
in others a choice would have to be made between competing standards. These standards
would be used along with the system requirements to prepare the system specifications.
A key to the standards determination would be the acceptance of an appropriate
international mobile data communications architecture.
d. Requirements Analysis
Concurrently with the determination of the equipment baseline should be
the establishment of the system requirements. The information provided in Chapters IV
and V of this thesis can form a foundation for the full analysis of the present and future
requirements needed to carry out the Coat Guard's missions as they relate to the NDS and
short-ranged C^. These requirements will later be used as the basis for writing the
specifications.
2
e. Engineering Assessment
While the baseline survey and requirements analysis are being conducted,
an engineering, assessment of each site should also be made. Configuration of the present
installations affect the functionality of the system. It appears from an examination of
Appendix B that many problems with VHF-FM coverage "holes" might be a problem
with antennas instead of site locations. Use of directional antennas that point offshore
reduces their effectiveness for onshore areas, including rivers, sheltered "back" bays, and
other areas where CG units may operate. Engineering studies performed at this stage may
solve many coverage problems without requiring the expense and problems involved with
installing additional sites.
This analysis would also determine which NDS sites needed to be
remoted to COTPs to provide full AOR coverage. Site surveys for additional remote
control units and/or remote transceiver sites should be performed at this time and prepar-
ations made for installation of the additional equipment.
f. Systems Research
Finally, there needs to be some preliminary research performed to solve
some of the potential problems that have been discussed in this thesis. These problems
include RDF antenna location/interference.
A test should be made of the interference caused by nearby emitters on
RDF antennas optimized and limited to the 120 MHz - 165 MHz frequency range.
Problems experienced by the FCC with their broadband RDF antennas and systems may
not affect the narrower frequency band with which the CG would be working.
92
Dependent surveillance using available DSC equipment should be
investigated. This ability to determine the location of underway CG units is valuable for
use with both the GDOC system and with the data network. The creation of a prototype
DSC controller that would periodically send the vessel's position and operational status
to the Group would provide a basis for a system-Wide adoption of the technology.
Another area of examination should be routing algorithms and addressing
to enable dynamic routing of packets and traffic from the HDN to the underway units via
the VHF-FM data network. If a vessel transmits its location periodically as part of
dependent surveillance, that transmission can be used to determine the return pathway for
data being sent to the unit. This routing, stored in a routing table, would eliminate the
need for communications shifts and make the network seamless.
2. | Phase II - System Definition
a. Specification Generation
Once Phase I has been completed, the established requirements and
selected standards should be used to write the system specifications. Compatibility with
the existing base of public VHF-FM radios and C.G.-owned DES radios will have to be
considered.
b. Engineering Modifications
Once the engineering analysis has been completed, it should be used to
solve NDS coverage problems prior to the installation of the new equipment. Upgrading
all sites to the baseline minimum for bonding, cable size, etc. may correct many perceived
J3
system problems. As previously noted, many of the AOR coverage problems experienced
by the system users may also be due to use of the wrong antennas or power levels.
Solving these problems by redirecting antennas, replacing directional antennas with
omnidirectional antennas or increasing the output power would prevent the costly
installation of additional sites.
At this time, the additional remote control units would be installed at the
COTPs to provide them with access to all the NDS sites covering their AORs, and any
additional remote transceiver sites would be installed.
c. Specification Publication
Once the systems have been brought up to baseline level and the
deficiencies corrected through better enginecring, it should be time to publish the
specifications and permit vendors to engineer their products to fulfill the requirements.
The emphasis should be on system modularity. Unlike the present system, where
Motorola has the monopoly on electronic equipment, the new system can be designed to
be made of separate modules that arc able to communicate and interact. The DSC
equipment, data transceiver, and RDF hardware can all come from non-Motorola sources
and thereby increase the competitive nature of the procurement. The modularity should
also be considered if the entire system is not to be procured at once, i.c., if the DES
transceiver and DSC transceivers are to be purchased now, but the RDF equipment and
data transceiver were to be purchased later as funds allowed.
94
3. Phase III - System Prototype
a. Prototype Installation
With a major system such as the NDS, it would be advantageous to be
able to install prototypes for evaluation prior to deciding on a final system. It would be
best to install prototypes from different vendors at different Groups or Districts, and
operate them concurrently to compare performance. The prototypes would enable the
individual system components to interact for the entire system to be operated by the users.
Feedback from the users would be provided for the next step, the prototype evaluation.
b. Prototype Evaluation
Once the prototypes are installed, they would be operated for a period of
tme to determine whether they fulfilled the specifications as written. Operational capa-
bilities would be determined for each system. Vendors would be given an opportunity
to correct discrepancies and modify their systems for better operations.
c. System Selection
Once the prototype evaluation was completed, the Project Manager would
then select the final system. Modifications to the prototype based upon its evaluation
results would be made prior to full-scale development.
4. Phase IV - System Installation
a. System Installation
The selected system would be procured and preparations made for its
installation. Installation would have to be performed in a manner to prevent the loss of
95
radio coverage in any one arca for longer than a few hours. Even thcn, alternate coverage
would have to be provided. System installation should be performed one Group at a time,
with the entire Group being converted from the old system to the new system at once.
Installation throughout the entire District should be completed before commencing at
another District, in order to provide compatibility and consistency within each District.
b. Initial System Evaluation
Prior to final acceptance of the systems at each site, an evaluation of the
system should be made. Quality of installation, availability and timeliness of main-
tenance, and reliability of the system should be evaluated. Problems with system
dependability should be addressed and CG-wide modifications made if necessary to
correct the problems.
S. | Phase V - System Evaluation
Once the entire system has been installed and operational for a few years, an
evaluation should be performed. This evaluation would be conducted with the purpose
of determining shortfalls in the system and recommending modifications. Periodic
reevaluations of the system, resulting in system upgrades, would permit the new NDS to
provide a high level of service throughout its life span.
96
tə
10.
LL
REFERENCES
United States Coast Guard, National VHF-FM Distress System, Commandant
Instruction 11120.3A, 29 April 1975.
Interdepartment Radio Advisory Committee, Minutes of Meeting of 3, 4, and 5
November 1948, Doc. #30276-1/49.
Office of Telecommunications Policy, Report of Ad Hoc Committee 125
(Reconstituted), Doc. #15624/1-1.9111/1.9.1255, March 1973.
Interdepartment Radio Advisory Committee, National VHF-FM Radiotelephone
Safety and Distress System Frequency Requirements in the Band 156-162 MHz,
Memorandum for the Executive Secretary, IRAC Doc. 15690/1-1.125, 5 April 1973.
Title 14 United States Code Sec. 2.
International Telecommunications Union, /TU Manual For Use By The Maritime
Mobile -Satellite Services, 1982 ed. 1985 rev.
United States Coast Guard, Coast Guard Telecommunications Manual, Commandant
Instruction M2000.3b, 4 April 1988.
United States Coast Guard, Coast Guard Telecommunications Plan, Commandant
Instruction M2000.4A, 20 April 1988.
National Technical Information Agency, Report 80-52, The Coverages of the MF
and VHF Maritime Distress Communications Systems, October 1980.
Glidden, W.C., "VHF-FM High Level Site Integrated Message Network," paper
presented to Naval Postgraduate School class CM3112, June 1990.
Commander, Coast Guard Group Grand Haven, MI rapidraft letter 2000 to
Commander (osr) Ninth Coast Guard District, Subject: Group Grand Haven High
Level Sites, 10 August 1990.
97
13.
14.
lə
16.
17.
18.
19:
211
Commander, Coast Guard Group Detroit, MI letter 2904 to Commander (ttm), Ninth
Coast Guard District, Subject: VHF-FM Distress Communications Study, 20 August
1985.
Commander, Coast Guard Group Mobile, AL letter 10550 to Commander (tts-1),
Coast Guard Maintenance and Logistics Command Atlantic, Subject: Additional
VHF-FM Communications Sites, 11 October 1988.
Commander (d), Fourteenth Coast Guard District letter 2000 to Commandant (G-
CPE), Subject: Planning Proposal to Revamp Guam VHF-FM System, dated 24
January 1990.
Presidential Directive 24.
National Security Director Directive-145.
United States Coast Guard Information Systems Center, Laboratory Test Results,
Project 4529 2660L, Low Cost Packet/SITOR Communications, 10 May 1990.
United States Coast Guard Electronics Engineering, Center, Project 4D1-1119.7W
Statement of Work Geographical Tactical Computer, 17 July 1990.
United States Coast Guard, Future Global Maritime Distress and Safety System
(FGMDSS) Implementation Plan, Enclosure (11) to Commandant Instruction
M2000.4, dtd 13 January 1986.
Chief, Search and Rescue Division (G-NRS) Memorandum to Chief, Telecom
munications Systems Division (G-TTS), Subject: Operational Requirement For
Shore-Based VHF-FM Direction Finders, 29 January 1990.
Federal Communications Commission, Temporary Waiver of the Maritime Service
Rules (Part 80) to Permit Use of VHF Maritime Channel 9 as a Secondary Calling
Channel in Boston Harbor, DA90-1110, released 21 August 1990.
98
26.
D.
28.
30.
Representative Studds, (D. MA), HR 4623, 4 Bill to Amend Title 14, United States
Code, to Impose Penalties for Inducing the Coast Guard to Render Aid Under False
Pretenses, to Impose Liability for Costs Incurred by the Coast Guard in Rendering
That Aid, and to Authorize Appropriations for Use for Acquiring Direction Finding
Equipment for the Coast Guard, 24 April 1990.
Sanders, M., Cramblitt, F., Harding, D., and Bergstrom, S., Very High Frequency
Radio Direction Finding SAR Data an Cost Benefit Analysis Report, RJO, 15 May
1986.
Coast Guard Academy Center For Advanced Studies, Letter 2000: to Commandant,
United States Coast Guard, Subject: VHF-DF Proposal/Solicitation For Funding,
25 March 1991.
Buddenberg, R., Draft Automated Dependent Surveillance Testbed Preliminary
Statement of Work, undated.
USCG Office of Research and Development, Report CG-D-9-87, Test and
Evaluation Report, Graphical Analysis, Archiving and Display Station (GAADS),
April 1987.
U.S. Department of Transportation Research and Special Programs Administration,
Transportation Systems Center, Report CG-D-28-78, An Evaluation of
Shore - Based Radio Direction Finding, September 1978.
Commander, First Coast Guard District letter 5830/190INRO11 to file, Subject:
Informal SAR Case Study and Claims Litigation Investigation into the
Circumstances Surrounding the Fishing Vessel SOL E MAR (U.S.) Reported
Overdue on 30 March 1990 in the Waters South of Nomans Land, 11 July 1990.
ST Systems Corporation, Very High Frequency Direction Finder System, application
note AN-4, undated.
Hamalainen, O., Jansen, T., Markstrom, K., Wedervang, B., "Implementation of the
Digital Selective Calling System in the Nordic Countries,” unpublished paper
provided by Ross Engineering, January 1991.
99
31.
55
34.
35.
36.
OF)
CCIR XVIIth Plenary Assembly Draft Recommendation 493-3, Mod F, Digital
Selective- Calling System for Use in the Maritime Mobile Service, Document
#8/1037-E, 1990.
Decker, J.W., 4 VHF-FM Digital Selective Calling System Mathematical Model
Using Grade of Service Criteria, Master's Thesis, Naval Postgraduate School,
Monterey, California, September 1985.
Network Analysis Corporation Report AD-8016 577, Third Semiannual Technical
Report for the Project: The Practical Impact of Recent Computer Advances on the
Analysis amd Design of Large Scale Networks, June 1974.
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Report for the Project: The Practical Impact of Recent Computer Advances on the
Analysis amd Design of Large Scale Networks, December 1974.
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100
APPENDIX A
ORIGINAL NATIONAL DISTRESS SYSTEM DESIGN CRITERIA
A. Operational Concept Influencing Design Performance.
(1) Each base station must have the following capabilities:
(a) Each high elevation installation must be engineered to optimize the
receiving ability of the site. Minimum design requirements must provide for a 1 watt
signal radiated from a unity gain antenna 6 ft. above mean low water, 20 NM offshore
to be discernible at a typical base station. The strength of this signal should be "Readable
with only Occasional Repetition: (Circuit Merit 3). Enclosed or semi-enclosed bodies
of water must have 100% coverage for this minimum condition. For inland rivers, the
system will be planned On the basis of a 25 watt signal from mean low water instead of
the 1 watt signal discussed above.
(b) The siting will make maximum use of existing tower structures and
terrain to minimize tower erection costs.
(c) Some sites may provide even greater than 20 miles coverage in order to
reduce the total number of stations. Site separation must be consistent with anticipated
message traffic volume. Systems must be designed to prevent message traffic in arcas
of high boating concentrations from dominating the receiver and reducing wide area
101
coverage due to the capture effect. Remote receivers on the periphery of the coverage
arca may be employed to prevent this.
(d) The antenna systems must be designed primarily to provide the greatest
gain to weak incoming signals from ships and boats while providing the maximum
suppression of noise coming from land areas. Secondarily, the antennas should provide
maximum power gain to the required operating areas. It is expected that the antennas of
highest performance characteristics consistent with the present state-of-the-art, cost and
mechanical constraints will be employed.
(e) To insure maximum detection of incoming signals, system signal loss
should be minimized. On certain very high towers, measures should be taken to provide
the least possible cabling loss. In these cases, the height gain and line loss must be
rationalized.
(f) each base station will normally require at least a 6 channel capability with
a separate guard receiver. Exceptions to this will be examined on a case by case basis.
The system should be configured so the transceiver can operate in a simplex mode with
the guard receiver set on channel 16 operating with the guard receiver set on channel 16
operating in a receive only mode and muted when the transmitter is keyed. Guard
receivers will not be provided on inland rivers unless specifically authorized.
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